题解

O(1)拿下

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n,m;
    cin>>n>>m;
    if(n<m){
        int c=n;
        n=m;
        m=c;
    }
    int a=n-m;
    int b=a*(a+1)/2;
    cout<<b-n;
    return 0;
}