P1102 A-B 数对对数组升序排序,枚举A (A-B=C)问题转化为对于A在A之前找等于(A-C)的值的个数,可以用二分做 复杂度:(O(nlogn)) #include<iostream> #include<algorithm> using namespace std; #define LL long long const int N = 200010; int a[N]; int n, c; int main(){ cin >> n >...