#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <iostream>
#include <vector>
#include <fstream>
#include <memory>
#include <cctype>
using namespace std;
#include <algorithm>
#include <cassert>
#include <complex>
#include <cstring>
#include <memory>
#include <string>
#include <vector>
using namespace std;
template <class T> struct is_iterator {
template <class U, typename enable_if<!is_convertible<U, const char*>::value, int>::type = 0>
constexpr static auto has_indirection(int) -> decltype(*declval<U>(), bool()) { return true; }
template <class> constexpr static bool has_indirection(long) { return false; }
constexpr static bool value = has_indirection<T>(0);
};
using uint = unsigned int;
// Buffer size should be 2^12 or 2^13 for optimal performance with files.
const uint BUFFER_SIZE = 1 << 12;
// Maximum possible length of a string representing primitive type
// assuming we won't encounter huge double values.
const uint MAX_LENGTH = 1 << 7;
namespace Detail {
struct Width { uint value; };
struct Fill { char value; };
struct Base { uint value; };
struct Precision { uint value; };
struct Delimiter { const char* value; };
} // namespace Detail
Detail::Width setWidth(uint value = 0) { return {value}; }
Detail::Fill setFill(char value = ' ') { return {value}; }
Detail::Base setBase(uint value = 10) { assert(2 <= value && value <= 36); return {value}; }
Detail::Precision setPrecision(uint value = 9) { assert(value < MAX_LENGTH); return {value}; }
Detail::Delimiter setDelimiter(const char* value = " ") { return {value}; }
/******************************* input classes ********************************/
class InputDevice {
protected:
const char* head;
const char* tail;
InputDevice(const char* head, const char* tail) : head(head), tail(tail), base(setBase().value) {}
virtual void fillInput() = 0;
inline char nextChar() {
if (__builtin_expect(head >= tail, false)) fillInput();
return *head++;
}
template <class I> int readUnsignedIntGeneral(I& arg, char c) {
I value = 0;
int length = 0;
for (;; ++length, c = nextChar()) {
if (isDigit(c)) c -= '0';
else if (isUpper(c)) c -= 'A' - 10;
else if (isLower(c)) c -= 'a' - 10;
else c = base;
if (c >= base) break;
value = base * value + c;
}
arg = value;
return --head, length;
}
template <class I> inline int readUnsignedInt(I& arg, char c) {
if (__builtin_expect(base > 10, false)) return readUnsignedIntGeneral(arg, c);
I value = 0;
int length = 0;
for (; static_cast<unsigned char>(c - '0') < base; ++length, c = nextChar())
value = base * value + c - '0';
arg = value;
return --head, length;
}
template <class I> inline bool readSignedInt(I& arg, char c) {
bool negative = c == '-';
if (negative) c = nextChar();
typename make_unsigned<I>::type unsignedArg;
if (readUnsignedInt(unsignedArg, c) == 0) return false;
arg = negative ? ~static_cast<I>(unsignedArg - 1) : static_cast<I>(unsignedArg);
return true;
}
template <class F> bool readFloatingPoint(F& arg, char c) {
bool negative = c == '-';
if (negative) c = nextChar();
unsigned long long integerPart;
if (readUnsignedInt(integerPart, c) == 0) return false;
arg = static_cast<F>(integerPart);
if (nextChar() == '.') {
unsigned long long fractionalPart = 0;
int fractionalLength = readUnsignedInt(fractionalPart, nextChar());
if (fractionalLength > 0) {
unsigned long long basePower = 1;
for (; fractionalLength; --fractionalLength) basePower *= base;
arg += static_cast<F>(fractionalPart) / basePower;
}
} else --head;
if (negative) arg = -arg;
return true;
}
public:
uint base;
InputDevice(InputDevice const&) = delete;
InputDevice& operator = (InputDevice const&) = delete;
static inline bool isSpace(char c) { return static_cast<unsigned char>(c - '\t') < 5 || c == ' '; }
static inline bool isDigit(char c) { return static_cast<unsigned char>(c - '0') < 10; }
static inline bool isUpper(char c) { return static_cast<unsigned char>(c - 'A') < 26; }
static inline bool isLower(char c) { return static_cast<unsigned char>(c - 'a') < 26; }
static inline bool isOneOf(char c, const char* str) { return strchr(str, c) != nullptr; }
void putBack() { --head; } // can be called only once directly after successfully reading a character
inline bool readChar(char& arg) {
if (__builtin_expect(head >= tail, false)) {
fillInput();
if (__builtin_expect(head >= tail, false)) return arg = '\0', false;
}
return arg = *head++, true;
}
template <class UnaryPredicate>
inline char skipCharacters(UnaryPredicate isSkipped) {
char c;
do { c = nextChar(); } while (isSkipped(c));
return c;
}
inline char skipCharacters() { return skipCharacters(isSpace); }
template <class UnaryPredicate>
inline int readString(char* arg, int limit, UnaryPredicate isTerminator) {
skipCharacters(isTerminator);
// put back first non-skipped character, reserve space for null character
int charsRead = 0;
for (--head, --limit; head < tail; fillInput()) {
ptrdiff_t chunkSize = find_if(head, min(tail, head + limit - charsRead), isTerminator) - head;
arg = copy_n(head, chunkSize, arg);
head += chunkSize;
charsRead += chunkSize;
if (chunkSize == 0 || head < tail) break;
}
return *arg = '\0', charsRead;
}
inline int readString(char* arg, int limit, const char* terminators) {
if (!*terminators) return readString(arg, limit, InputDevice::isSpace);
return readString(arg, limit, [terminators](char c) { return InputDevice::isOneOf(c, terminators); });
}
// property setters
inline bool read(Detail::Base newBase) { base = newBase.value; return true; }
// primitive types
inline bool read() { return true; }
inline bool read(char& arg) { return readChar(arg); }
template <class I> inline typename enable_if<is_integral<I>::value && is_unsigned<I>::value,
bool>::type read(I& arg) { return readUnsignedInt(arg, skipCharacters()) > 0; }
template <class I> inline typename enable_if<is_integral<I>::value && is_signed<I>::value,
bool>::type read(I& arg) { return readSignedInt(arg, skipCharacters()); }
template <class F> inline typename enable_if<is_floating_point<F>::value,
bool>::type read(F& arg) { return readFloatingPoint(arg, skipCharacters()); }
// characters skip
inline bool read(const char& arg) { skipCharacters([arg](char c) { return arg != c; }); return true; }
inline bool read(const char* arg) {
if (*arg) skipCharacters([arg](char c) { return InputDevice::isOneOf(c, arg); });
else skipCharacters();
return putBack(), true;
}
inline bool read(bool (*isSkipped)(char)) { skipCharacters(isSkipped); putBack(); return true; }
// strings
template <class I, class Terminator, class... Ts> inline typename enable_if<is_integral<I>::value,
bool>::type read(char* arg, I limit, Terminator terminator, Ts&&... args) {
readString(arg, static_cast<int>(limit), terminator);
return read(forward<Ts>(args)...);
}
template <class I> inline typename enable_if<is_integral<I>::value,
bool>::type read(char* arg, I limit) { return read(arg, limit, ""); }
template <class... Ts>
inline bool read(char* first, char* last, Ts&&... args) {
return read(first, static_cast<int>(last - first), forward<Ts>(args)...);
}
template <int N, class... Ts>
inline bool read(char (&arg)[N], Ts&&... args) { return read(static_cast<char*>(arg), N, forward<Ts>(args)...); }
template <class Terminator, class... Ts>
inline bool read(string& arg, Terminator terminator, Ts&&... args) {
for (int length = 16, last = 0;; last += length, length <<= 1) {
arg.resize(last + length);
int charsRead = readString(&arg[last], length + 1, terminator);
if (charsRead < length) {
arg.resize(last + charsRead);
return read(forward<Ts>(args)...);
}
}
}
inline bool read(string& arg) { return read(arg, ""); }
// complex types and ranges
template <class T1, class T2>
inline bool read(pair<T1, T2>& arg) { return read(arg.first, arg.second); }
template <class T>
inline bool read(complex<T>& arg) {
T real, imag;
if (!read(real, imag)) return false;
arg.real(real), arg.imag(imag);
return true;
}
template <class T>
inline bool read(vector<T>& arg) {
uint n;
if (!read(n)) return false;
arg.resize(n);
return read(arg.begin(), arg.end());
}
template <class Iterator, class... Ts> inline typename enable_if<is_iterator<Iterator>::value,
bool>::type read(Iterator first, Iterator last, Ts&&... args) {
for (; first != last; ++first) if (!read(*first)) return false;
return read(forward<Ts>(args)...);
}
template <class Iterator, class I, class... Ts>
inline typename enable_if<is_iterator<Iterator>::value && is_integral<I>::value,
bool>::type read(Iterator first, I count, Ts&&... args) { return read(first, first + count, forward<Ts>(args)...); }
// generic forwarding
template <class T>
inline auto read(T& arg) -> decltype(arg.read(*this)) { return arg.read(*this); }
template <class T0, class T1, class... Ts>
inline typename enable_if<!is_iterator<T0>::value && !is_convertible<T0, char*>::value,
bool>::type read(T0&& arg0, T1&& arg1, Ts&&... args) {
return read(forward<T0>(arg0)) && read(forward<T1>(arg1), forward<Ts>(args)...);
}
};
class InputFile : public InputDevice {
FILE* file;
bool lineBuffered;
bool owner;
char buffer[BUFFER_SIZE];
void fillInput() override {
head = buffer;
*buffer = '\0';
if (__builtin_expect(!lineBuffered, true)) {
tail = head + fread(buffer, 1, BUFFER_SIZE, file);
} else {
tail = head;
if (fgets(buffer, BUFFER_SIZE, file)) while (*tail) ++tail;
}
}
public:
InputFile(FILE* file = stdin, bool lineBuffered = true, bool takeOwnership = false)
: InputDevice(buffer, buffer) , file(file), lineBuffered(lineBuffered), owner(takeOwnership) {}
InputFile(const char* fileName) : InputFile(fopen(fileName, "r"), false, true) {}
~InputFile() { if (owner) fclose(file); }
};
// Picks up data appended to the string but doesn't handle reallocation.
class InputString : public InputDevice {
void fillInput() override { while (*tail) ++tail; }
public:
InputString(const string& s) : InputDevice(s.data(), s.data() + s.size()) {}
InputString(const char* s) : InputDevice(s, s + strlen(s)) {}
};
/******************************* output classes *******************************/
class OutputDevice {
protected:
char buffer[BUFFER_SIZE + MAX_LENGTH];
char* output;
char* end;
bool separate;
OutputDevice() : output(buffer), end(buffer + BUFFER_SIZE + MAX_LENGTH), separate(false)
, width(setWidth().value), fill(setFill().value), base(setBase().value), precision(setPrecision().value)
, delimiter(setDelimiter().value) { computeBasePower(); }
virtual void writeToDevice(uint count) = 0;
inline void flushMaybe() {
if (__builtin_expect(output >= buffer + BUFFER_SIZE, false)) {
writeToDevice(BUFFER_SIZE);
output = copy(buffer + BUFFER_SIZE, output, buffer);
}
}
void computeBasePower() {
basePower = 1;
for (uint i = 0; i < precision; ++i) basePower *= base;
}
template <class I> inline char* writeUnsignedInt(I arg, char* last) {
if (__builtin_expect(arg == 0, false)) *--last = '0';
if (__builtin_expect(base == 10, true)) {
for (; arg; arg /= 10) *--last = '0' + arg % 10;
} else for (; arg; arg /= base) {
I digit = arg % base;
*--last = digit < 10 ? '0' + digit : 'A' - 10 + digit;
}
return last;
}
template <class I> inline char* writeSignedInt(I arg, char* last) {
auto unsignedArg = static_cast<typename make_unsigned<I>::type>(arg);
if (arg < 0) {
last = writeUnsignedInt(~unsignedArg + 1, last);
*--last = '-';
return last;
}
return writeUnsignedInt(unsignedArg, last);
}
template <class F> char* writeFloatingPoint(F arg, char* last) {
bool negative = signbit(arg);
if (negative) arg = -arg;
if (isnan(arg)) for (int i = 0; i < 3; ++i) *--last = i["NaN"];
else if (isinf(arg)) for (int i = 0; i < 3; ++i) *--last = i["fnI"];
else {
auto integerPart = static_cast<unsigned long long>(arg);
auto fractionalPart = static_cast<unsigned long long>((arg - integerPart) * basePower + F(0.5));
if (fractionalPart >= basePower) ++integerPart, fractionalPart = 0;
char* point = last - precision;
if (precision > 0) {
::fill(point, writeUnsignedInt(fractionalPart, last), '0');
*--point = '.';
}
last = writeUnsignedInt(integerPart, point);
}
if (negative) *--last = '-';
return last;
}
inline int writeT(char* first) {
int delimiterLenght = separate ? writeDelimiter() : 0;
separate = true;
uint charsWritten = static_cast<uint>(end - first);
if (__builtin_expect(charsWritten < width, false))
charsWritten += writeFill(width - charsWritten);
output = copy(first, end, output);
flushMaybe();
return delimiterLenght + static_cast<int>(charsWritten);
}
inline int writeFill(uint count) {
int charsWritten = static_cast<int>(count);
if (__builtin_expect(output + count + MAX_LENGTH < end, true)) {
if (count == 1) *output++ = fill;
else output = fill_n(output, count, fill);
} else for (uint chunkSize = static_cast<uint>(buffer + BUFFER_SIZE - output);; chunkSize = BUFFER_SIZE) {
if (chunkSize > count) chunkSize = count;
output = fill_n(output, chunkSize, fill);
flushMaybe();
if ((count -= chunkSize) == 0) break;
}
return charsWritten;
}
public:
uint width;
char fill;
uint base;
uint precision;
unsigned long long basePower;
string delimiter;
OutputDevice(OutputDevice const&) = delete;
OutputDevice& operator = (OutputDevice const&) = delete;
virtual ~OutputDevice() {};
inline int writeChar(char arg) { separate = false; *output++ = arg; flushMaybe(); return 1; }
inline int writeString(const char* arg, size_t length, bool checkWidth = true) {
separate = false;
uint count = static_cast<uint>(length);
int charsWritten = static_cast<int>(count) + (checkWidth && count < width ? writeFill(width - count) : 0);
if (__builtin_expect(output + count + MAX_LENGTH < end, true)) {
if (count == 1) *output++ = *arg;
else output = copy_n(arg, count, output);
} else for (uint chunkSize = static_cast<uint>(buffer + BUFFER_SIZE - output);; chunkSize = BUFFER_SIZE) {
if (chunkSize > count) chunkSize = count;
output = copy_n(arg, chunkSize, output);
flushMaybe();
if ((count -= chunkSize) == 0) break;
arg += chunkSize;
}
return charsWritten;
}
inline int writeDelimiter() { return writeString(delimiter.c_str(), delimiter.size(), false); }
inline void flush() {
writeToDevice(static_cast<uint>(output - buffer));
output = buffer;
}
// property setters
inline int write(Detail::Width newWidth) { width = newWidth.value; return 0; }
inline int write(Detail::Fill newFill) { fill = newFill.value; return 0; }
inline int write(Detail::Base newBase) { base = newBase.value; computeBasePower(); return 0; }
inline int write(Detail::Precision newPrecision) {
precision = newPrecision.value; computeBasePower(); return 0;
}
inline int write(Detail::Delimiter newDelimiter) { delimiter = newDelimiter.value; return 0; }
// primitive types
inline int write() { return 0; }
inline int write(char arg) { return writeChar(arg); }
template <class I> inline typename enable_if<is_integral<I>::value && is_unsigned<I>::value,
int>::type write(I arg) { return writeT(writeUnsignedInt(arg, end)); }
template <class I> inline typename enable_if<is_integral<I>::value && is_signed<I>::value,
int>::type write(I arg) { return writeT(writeSignedInt(arg, end)); }
template <class F> inline typename enable_if<is_floating_point<F>::value,
int>::type write(F arg) { return writeT(writeFloatingPoint(arg, end)); }
// complex types
inline int write(const char* arg) { return writeString(arg, strlen(arg)); }
template <int N>
inline int write(char (&arg)[N]) { return writeString(arg, strlen(arg)); }
inline int write(const string& arg) { return writeString(arg.c_str(), arg.size()); }
template <class T1, class T2>
inline int write(const pair<T1, T2>& arg) {
int charsWritten = write(arg.first);
charsWritten += writeDelimiter();
return charsWritten + write(arg.second);
}
template <class T>
inline int write(const complex<T>& arg) { return write(real(arg), imag(arg)); }
// ranges
template <class Iterator, class... Ts> inline typename enable_if<is_iterator<Iterator>::value,
int>::type write(Iterator first, Iterator last, Ts&&... args) {
int charsWritten = 0;
for (; first != last; charsWritten += ++first == last ? 0 : writeDelimiter()) charsWritten += write(*first);
return charsWritten + write(forward<Ts>(args)...);
}
template <class Iterator, class I, class... Ts>
inline typename enable_if<is_iterator<Iterator>::value && is_integral<I>::value,
int>::type write(Iterator first, I count, Ts&&... args) { return write(first, first + count, forward<Ts>(args)...); }
// generic forwarding
template <class T>
inline auto write(const T& arg) -> decltype(arg.write(*this)) { return arg.write(*this); }
template <class T0, class T1, class... Ts> inline typename enable_if<!is_iterator<T0>::value,
int>::type write(T0&& arg0, T1&& arg1, Ts&&... args) {
int charsWritten = write(forward<T0>(arg0));
return charsWritten + write(forward<T1>(arg1), forward<Ts>(args)...);
}
};
class OutputFile : public OutputDevice {
FILE* file;
bool owner;
void writeToDevice(uint count) override {
fwrite(buffer, 1, count, file);
fflush(file);
}
public:
OutputFile(FILE* file = stdout, bool takeOwnership = false) : file(file), owner(takeOwnership) {}
OutputFile(const char* fileName) : OutputFile(fopen(fileName, "w"), true) {}
~OutputFile() override { flush(); if (owner) fclose(file); }
};
class OutputString : public OutputDevice {
string& str;
void writeToDevice(uint count) override { str.append(buffer, count); }
public:
OutputString(string& str) : OutputDevice(), str(str) {}
~OutputString() override { flush(); }
};
unique_ptr<InputDevice> input;
unique_ptr<OutputDevice> output;
template <class... Ts> inline bool read(Ts&&... args) { return input->read(forward<Ts>(args)...); }
template <class... Ts> inline int write(Ts&&... args) { return output->write(forward<Ts>(args)...); }
template <class... Ts> inline int writeln(Ts&&... args) { return write(forward<Ts>(args)..., '\n'); }
void flush() { output->flush(); }
class Graph {
private:
struct Edge {
int from, to;
Edge() { }
Edge(const int _from, const int _to) : from(_from), to(_to) { }
};
template<typename T>
struct Range {
struct Iterator {
T& operator *() const { return *iter; }
bool operator !=(const Iterator& rhs) const { return iter != rhs.iter; }
void operator ++() { ++iter; }
T* operator +(int i) const { return iter + i; }
size_t operator -(const Iterator& rhs) const { return iter - rhs.iter; }
T* iter;
};
Range(T* _first, T* _last) : first({_first}), last({_last}) { }
T operator[] (const int i) { return *(first + i); }
size_t size() const { return last - first; }
Iterator& begin() { return first; }
Iterator& end() { return last; }
Iterator first, last;
};
public:
Range<int> operator [](int u) {
return Range<int>(&edges[offset[u]], &edges[offset[u + 1]]);
}
Graph() = default;
Graph(const int N, const int M=0) : n(N), offset(N + 1) {
if (M > 0) { in.reserve(M); }
}
void AddEdge(int x, int y) { in.emplace_back(x, y); }
void Init() {
edges.resize(in.size());
for (auto&& e : in) { offset[e.from] += 1; }
for (int i = 1; i <= n; i += 1) {
offset[i] += offset[i - 1];
}
for (auto&& e : in) {
edges[--offset[e.from]] = e.to;
}
in.clear();
}
size_t size() const {
return (size_t)n;
}
private:
int n;
vector<int> offset, edges;
vector<Edge> in;
};
class SchieberVishkinLCA {
private:
static inline int lsb(int value) {
return value & -value;
}
static inline int msb(int v) {
v |= v >> 1;
v |= v >> 2;
v |= v >> 4;
v |= v >> 8;
v |= v >> 16;
return v >> 1;
}
public:
SchieberVishkinLCA() = default;
SchieberVishkinLCA(Graph& G, int root) : idx(G.size()), max_idx(G.size()), ancestor_height(G.size()), path_parent(G.size()) {
int n = G.size();
vector<int> parent(n), vertices(n);
auto Dfs = [&]() {
int stack_size = 1, euler_idx = 1;
vertices[0] = root;
parent[root] = -1;
while (stack_size > 0) {
const int node = vertices[--stack_size];
idx[node] = euler_idx++;
for (auto&& son : G[node]) {
if (parent[node] != son) {
parent[son] = node;
vertices[stack_size++] = son;
}
}
}
};
auto Bfs = [&]() {
int q_front = 0, q_end = 1;
vertices[0] = root;
parent[root] = -1;
while (q_front != q_end) {
const int node = vertices[q_front++];
for (auto&& son : G[node]) {
if (parent[node] != son) {
parent[son] = node;
vertices[q_end++] = son;
}
}
}
};
Dfs(); Bfs();
max_idx = idx;
for (int i = n - 1; i > 0; i -= 1) {
const int node = vertices[i];
if (lsb(max_idx[parent[node]]) < lsb(max_idx[node])) {
max_idx[parent[node]] = max_idx[node];
}
}
ancestor_height[root] = 0;
for (int i = 1; i < n; i += 1) {
const int node = vertices[i];
ancestor_height[node] = ancestor_height[parent[node]] | lsb(max_idx[node]);
}
path_parent[idx[root] - 1] = root;
for (int i = 0; i < n; i += 1) {
const int node = vertices[i];
for (auto&& son : G[node]) {
if (parent[node] == son) {
continue;
}
path_parent[idx[son] - 1] = (max_idx[node] == max_idx[son]) ? path_parent[idx[node] - 1] : node;
}
}
}
int Query(int x, int y) const {
const int Ix = max_idx[x], Iy = max_idx[y];
const int hIx = lsb(Ix), hIy = lsb(Iy);
const int msb_mask = msb((Ix ^ Iy) | hIx | hIy);
const int mask = lsb(ancestor_height[x] & ancestor_height[y] & ~msb_mask);
int left, right;
if (mask == hIx) {
left = x;
} else {
const int kMask = msb(ancestor_height[x] & (mask - 1));
left = path_parent[((idx[x] & ~kMask) | (kMask + 1)) - 1];
}
if (mask == hIy) {
right = y;
} else {
const int kMask = msb(ancestor_height[y] & (mask - 1));
right = path_parent[((idx[y] & ~kMask) | (kMask + 1)) - 1];
}
return (idx[left] < idx[right]) ? left : right;
}
private:
vector<int> idx, max_idx, ancestor_height, path_parent;
};
int main() {
#ifdef INFOARENA
input.reset(new InputFile("lca.in", false));
output.reset(new OutputFile("lca.out"));
#else
input.reset(new InputFile(stdin, false));
output.reset(new OutputFile());
#endif
int n, m; read(n, m);
Graph G(n, n - 1);
for (int i = 1; i < n; i += 1) {
int parent; read(parent); parent -= 1;
G.AddEdge(parent, i);
}
G.Init();
SchieberVishkinLCA LcaSolver(G, 0);
for (int i = 0; i < m; i += 1) {
int x, y; read(x, y); x -= 1; y -= 1;
writeln(1 + LcaSolver.Query(x, y));
}
}