原题链接： 

方法很多，我用的是快排+二分，练习一下stl lower_bound这个函数。。。

1 #include
      
        2 #include
       
         3 #include
        
          4 #include
         
           5 #include
          
            6 using std::sort; 7 using std::lower_bound; 8 const int Max_N = 100010; 9 struct node {10     int v, id;11 }rec[Max_N];12 int arr[Max_N];13 bool cmp(node &a, node &b) {14     if (a.v == b.v) return a.id < b.id;15     return a.v < b.v;16 }17 int main() {18 #ifdef LOCAL19     freopen("in.txt", "r", stdin);20     freopen("out.txt", "w+", stdout);21 #endif22     int n, m, a, b, pos;23     while (~scanf("%d %d", &n, &m)) {24         for (int i = 0; i < n; i++) {25             scanf("%d", &rec[i].v);26             rec[i].id = i + 1;27         }28         sort(rec, rec + n, cmp);29         for (int i = 0; i < n; i++) arr[i] = rec[i].v;30         while (m--) {31             scanf("%d %d", &a, &b);32             pos = lower_bound(arr, arr + n, b) - arr;33             node &k = rec[pos + a - 1];34             if (k.v == b) printf("%d\n", k.id);35             else puts("0");36         }37     }38     return 0;39 }