Educational Codeforces Round 7-C. Not Equal on a Segment

原题链接

C. Not Equal on a Segment

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

You are given array a with n integers and m queries. The i-th query is given with three integers li, ri, xi.

For the i-th query find any position pi (li ≤ pi ≤ ri) so that api ≠ xi.

Input

The first line contains two integers n, m (1 ≤ n, m ≤ 2·105) — the number of elements in a and the number of queries.

The second line contains n integers ai (1 ≤ ai ≤ 106) — the elements of the array a.

Each of the next m lines contains three integers li, ri, xi (1 ≤ li ≤ ri ≤ n, 1 ≤ xi ≤ 106) — the parameters of the i-th query.

Output

Print m lines. On the i-th line print integer pi — the position of any number not equal to xi in segment [li, ri] or the value  - 1 if there is no such number.

Examples

input

6 41 2 1 1 3 51 4 12 6 23 4 13 4 2

output

26-14

类似RMQ问题

用dp[i][j]表示[i-1, i+(1<<j))这个区间内任意一个下标k,使num[k] != num[k-1],先用ST算法对dp数组进行预处理,

对于给定的区间l, r, 和x, 

1.l == r则直接判断num[l]和x是否相等.

2.l != r 用dp数组查询[l+1, r]中是否存在k, 使得num[k] != num[k-1],然后再用x和num[k]与num[k-1]比较

#include <bits/stdc++.h>#define maxn 200005using namespace std;int dp[maxn][20], num[maxn];int n, m;void RMQ(){for(int i = 1; (1<<i) <= n; i++)  for(int j = 2; (j + (1<<i)) <= n+1; j++){  int k1 = dp[j][i-1], k2 = dp[j+(1<<(i-1))][i-1];  if(num[k1] != num[k1-1])   dp[j][i] = dp[j][i-1];  else   dp[j][i] = dp[j+(1<<(i-1))][i-1];  }}int Query(int l, int r){int k = 0;while(1<<(k+1) <= r - l + 1) k++;int k1 = dp[l][k], k2 = dp[r-(1<<k)+1][k];if(num[k1] != num[k1-1])  return k1;else return k2;}int main(){//freopen("in.txt", "r", stdin);scanf("%d%d", &n, &m);for(int i = 1; i <= n; i++){scanf("%d", num+i);dp[i][0] = i;}RMQ();int l, r, x;while(m--){scanf("%d%d%d", &l, &r, &x);if(r == l){if(num[l] != x) printf("%d\n", l);else puts("-1");}else if(l != r){int k = Query(l+1, r);if(num[k] != x) printf("%d\n", k);else if(num[k-1] != x) printf("%d\n", k-1);else puts("-1");}}return 0;}