#include <bits/stdc++.h>
using namespace std;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n, m;
cin >> n >> m;
vector<int> a(n);
for (int i = 0; i < n; ++i ) cin >> a[i];
vector<int> prec(n, -1);
for (int i = 1; i < n; ++i){
if (a[i - 1] != a[i]) prec[i] = i - 1;
else prec[i] = prec[i - 1];
}
for (int i = 0; i < m; ++i){
int l, r, x;
cin >> l >> r >> x;
if (a[r - 1] != x) cout << r;
else if (prec[r - 1] >= l - 1) cout << prec[r - 1] + 1;
else cout << -1;
cout << "\n";
}
return 0;
}
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