Cod sursa(job #51292)

Utilizator scapryConstantin Berzan scapry Data 10 aprilie 2007 20:37:41
Problema Stramosi Scor 100
Compilator cpp Status done
Runda Arhiva de probleme Marime 1.4 kb
#include <stdio.h>
#include <string.h>

enum { maxn = 250001 };
int firstbit[maxn];
int onefb[maxn];

int n;
int dad[maxn];
int depth[maxn];
bool v[maxn];
int ans[20][maxn];

void precalc_firstbit()
{
	int i, bit = 0;

	for(i = 0; i < maxn; i++)
	{
		if(i >= (1 << bit)) bit++;
		firstbit[i] = bit - 1;
		onefb[i] = ~(1 << firstbit[i]);
	}
}

int calc(int node, int rank)
{
	if(rank > n) return 0;
	if(rank >= depth[node]) return 0;

	while(true)
	{
		if(rank == 0) return node;

		node = ans[ firstbit[rank] ][node];
		rank &= onefb[rank];
	}
}

void precalc(int node)
{
	if(v[node]) return;

	//terminal case - root
	if(dad[node] == 0)
	{
		depth[node] = 1;
	}
	else
	{
		precalc(dad[node]);

		depth[node] = depth[ dad[node] ] + 1;

		int i, now;

		ans[0][node] = dad[node];
		now = ans[0][node];
		
		for(i = 1; i < 31; i++)
		{
			ans[i][node] = ans[i - 1][now];
			if(ans[i][node] == 0) break; //all zero from now on
			now = ans[i][node];
		}
	}

	v[node] = true;
}

int main()
{
	int queries, i, who, rank;
	FILE *fi = fopen("stramosi.in", "r"),
	     *fo = fopen("stramosi.out", "w");
	if(!fi || !fo) return 1;

	fscanf(fi, "%d%d", &n, &queries);
	for(i = 1; i <= n; i++)
		fscanf(fi, "%d", &dad[i]);

	precalc_firstbit();

	for(i = 1; i <= n; i++)
		precalc(i);

	for(i = 0; i < queries; i++)
	{
		fscanf(fi, "%d %d ", &who, &rank);
		fprintf(fo, "%d\n", calc(who, rank));
	}
	
	fclose(fi);
	fclose(fo);
       	return 0;
}