solution

输出的是重复的差值，而非全部差值

#include<iostream>
#include<algorithm>
using namespace std;
const int maxn = 1e4 + 10;
int flag[maxn] = {0};
int main(){
	int n, x;
	scanf("%d", &n);
	for(int i = 1; i <= n; i++){
		scanf("%d", &x);
		flag[abs(i - x)]++;
	}
	for(int i = maxn - 1; i >= 0; i--){
		if(flag[i] > 1) printf("%d %d\n", i, flag[i]);
	}
	return 0;
}