AtCoder Beginner Contest 166 E.This Message Will Self-Destruct in 5s
題目鏈接
思維題,題意是找一對 使得 ,我們不妨設 ,移項得:,很容易想到用 存數,每次更新答案即可,AC代碼如下:
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
main()
{
int n;
cin>>n;
int a[n+1];
map<int,int>m;
ll ans=0;
for(int i=1;i<=n;i++){
cin>>a[i];
ans+=m[a[i]-i];
m[-a[i]-i]++;
}
cout<<ans;
return 0;
}