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

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;}