#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  vector<int> a(n);
  for (int &x : a) {
    scanf("%d", &x);
  }
  vector<int> b(n);
  b[0] = 1;
  for (int i = 1; i < n; ++i) {
    if (a[i] == a[i - 1]) {
      b[i] = b[i - 1];
    } else {
      b[i] = 1 - b[i - 1];
    }
  }
  vector<int> next0(n);
  vector<int> next1(n);
  next0[n - 1] = (b[n - 1] == 1 ? -1 : n - 1);
  for (int i = n - 2; i >= 0; --i) {
    if (b[i] == 1) {
      next0[i] = next0[i + 1];
    } else {
      next0[i] = i;
    }
  }
  next1[n - 1] = (b[n - 1] == 0 ? -1 : n - 1);
  for (int i = n - 2; i >= 0; --i) {
    if (b[i] == 0) {
      next1[i] = next1[i + 1];
    } else {
      next1[i] = i;
    }
  }
  while (m--) {
    int l, r, x;
    scanf("%d%d%d", &l, &r, &x);
    --l;
    --r;
    if (b[l] == 0) {
      if (next1[l] > r || next1[l] == -1) {
        if (x != a[l]) {
          printf("%d\n", l + 1);
        } else {
          printf("-1\n");
        }
      } else {
        if (a[next1[l]] == x) {
          printf("%d\n", l + 1);
        } else {
          printf("%d\n", next1[l] + 1);
        }
      }
    } else {
      if (next0[l] > r || next0[l] == -1) {
        if (x != a[l]) {
          printf("%d\n", l + 1);
        } else {
          printf("-1\n");
        }
      } else {
        if (a[next0[l]] == x) {
          printf("%d\n", l + 1);
        } else {
          printf("%d\n", next0[l] + 1);
        }
      }
    }
  }
  return 0;
}
