#include <bits/stdc++.h>
using namespace std;
int cnt[200005];
int main() {
  int i = 1, j, t, l, r, p, a, b, c, d, k, x, n, m, mix = 1, fact = 1, ans = 0;
  scanf("%d%d", &n, &m);
  int arr[n + 2];
  long long idx = 0;
  for (i = 1; i <= n; i++) {
    scanf("%d", &arr[i]);
    if (i == 1) continue;
    if (arr[i] == arr[i - 1])
      cnt[i] = cnt[i - 1];
    else
      cnt[i] = i - 1;
  }
  for (i = 0; i < m; i++) {
    scanf("%d%d%d", &l, &r, &x);
    if (arr[r] != x)
      ans = r;
    else
      ans = cnt[r];
    if (ans >= l)
      printf("%d\n", ans);
    else
      printf("-1\n");
  }
  return 0;
}
