STL UVA 11991 Easy Problem from Rujia Liu?

题目传送门

题意:训练指南P187

分析:用vector存id下标,可以用map,也可以离散化用数组存(发现不用离散化也可以)

map

#include <bits/stdc++.h>
using namespace std;

map<int, vector<int> >mp;

int main(void)	{
	int n, m;
	while (scanf ("%d%d", &n, &m) == 2)	{
		mp.clear ();
		for (int a, i=1; i<=n; ++i)	{
			scanf ("%d", &a);
			if (!mp.count (a))	mp[a] = vector<int> ();
			mp[a].push_back (i);
		}
		while (m--)	{
			int k, v;	scanf ("%d%d", &k, &v);
			if (!mp.count (v) || mp[v].size () < k)	puts ("0");
			else	printf ("%d
", mp[v][k-1]);
		}
	}

	return 0;
}

离散化

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 5;
vector<int> vec[N];
int a[N], A[N];

int main(void)	{
	int n, m;
	while (scanf ("%d%d", &n, &m) == 2)	{
		for (int i=1; i<=n; ++i)	vec[i].clear ();
		for (int i=1; i<=n; ++i)	{
			scanf ("%d", &a[i]);	A[i] = a[i];
		}
		sort (A+1, A+1+n);
		int nn = unique (A+1, A+1+n) - A - 1;
		for (int i=1; i<=n; ++i)	{
			a[i] = lower_bound (A+1, A+1+nn, a[i]) - A;
		}
		for (int i=1; i<=n; ++i)	{
			vec[a[i]].push_back (i);
		}
		for (int k, v, i=1; i<=m; ++i)	{
			scanf ("%d%d", &k, &v);
			v = lower_bound (A+1, A+1+nn, v) - A;
			if (vec[v].size () < k)	puts ("0");
			else	printf ("%d
", vec[v][k-1]);
		}
	}

	return 0;
}