1320A - Journey Planning - CodeForces Solution

#ifndef __KUTORI__
#define __KUTORI__

#include <map>
#include <iostream>
using namespace std;
typedef long long int64;

const int N = 2e5;
int b[N+5];

int main() {
    ios::sync_with_stdio(0); cin.tie(nullptr);
    int n, i; cin >> n;
    for (i = 1; i <= n; i++) cin >> b[i];
    // solve
    int64 ans = -1e9;
    map<int, int64> ATshayu;
    for (i = 1; i <= n; i++) {
        int v = b[i] - i;
        if (ATshayu.count(v) == 0) ATshayu[v] = b[i];
        else ATshayu[v] += b[i];
        ans = max(ans, ATshayu[v]);
    }
    cout << ans << "\n";
    return 0;
}

#endif