CodeFroces 817B. Makes And The Product(构造)

分类讨论下即可。

代码如下：

#include<iostream>#include<cstdio>#include<vector>#include<queue>#include<utility>#include<stack>#include<algorithm>#include<cstring>#include<string>#include<cmath>#include<set>#include<map>using namespace std;const int maxn = 1e5 + 5;int n, a[maxn];int main() {#ifndef ONLINE_JUDGE//freopen("in.txt", "r", stdin);//    freopen("out.txt", "w", stdout);#endifscanf("%d", &n);for(int i = 0; i < n; i++)scanf("%d", &a[i]);sort(a, a + n);if(a[0] == a[2]) {long long c = 3, j = 3;while(a[j] == a[2]) {j++, c++;}printf("%I64d\n", c * (c - 1) * (c - 2) / 6);} else if(a[0] == a[1]) {long long c = 1, j = 3;while(a[j] == a[2]) {j++, c++;}printf("%I64d\n", c);} else if(a[1] == a[2]) {long long c = 2, j = 3;while(a[j] == a[2]) {j++, c++;}printf("%I64d\n", c * (c - 1) / 2);} else {long long c = 1, j = 3;while(a[j] == a[2]) {j++, c++;}printf("%I64d\n", c);}return 0;}