UVA 11991 - Easy Problem from Rujia Liu?

题目链接

题意:给一个长度n的序列，有m询问，每个询问会问第k个出现的数字的下标是多少

思路:用map和vector搞，map[i][j]直接保存的就是数字i第j个出现，每次直接输出即可

代码：

#include <cstdio>
#include <cstring>
#include <vector>
#include <map>
using namespace std;

int n, m;

map<int, vector<int> > ans;

int main() {
    while (~scanf("%d%d", &n, &m)) {
	int a, b;
	ans.clear();
	for (int i = 1; i <= n; i++) {
	    scanf("%d", &a);
	    if (!ans.count(a)) ans[a] = vector<int> ();
	    ans[a].push_back(i);
	}
	while (m--) {
	    scanf("%d%d", &a, &b);
	    if (ans[b].size() < a) printf("0\n");
	    else printf("%d\n", ans[b][a - 1]);
	}
    }
    return 0;
}

11991 - Easy Problem from Rujia Liu?（基础数据结构)