#include <bits/stdc++.h>
using namespace std;
bool debug = 0;
int n, m, k;
int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};
string direc = "RDLU";
long long ln, lk, lm;
int pre[200055], a[200055];
void fmain() {
  scanf("%d%d", &n, &m);
  for (int(i) = 1; (i) <= (int)(n); (i)++) scanf("%d", a + i);
  pre[1] = 1;
  for (int i = 2; i <= n; i++) {
    if (a[i] == a[i - 1])
      pre[i] = pre[i - 1] + 1;
    else
      pre[i] = 1;
  }
  for (int l, r, x, i = 0, ans; i < m; i++) {
    scanf("%d%d%d", &l, &r, &x);
    ans = -1;
    if (a[r] != x)
      ans = r;
    else {
      if (r - pre[r] >= l) ans = r - pre[r];
    }
    printf("%d\n", ans);
  }
}
int main() {
  fmain();
  return 0;
}
