Codeforces #247 (Div. 2)　B. Shower Line

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暴力题，知道下一个排列：next_permutation()就好做了

b[1]-b[5]为１－５的全排列

则找出b的所有全排列，计算sum = a[b[1]][b[2]] + a[b[2]][b[1]] + a[b[2]][b[3]] + a[b[3]][b[2]] + 2*a[b[3]][b[4]] + 2*a[b[4]][b[3]] + 2*a[b[4]][b[5]]+2*a[b[5]][b[4]];的最大值即可

代码如下：

#include <cstdio>
#include <iostream>
#include <algorithm>
#define MAXN 110
#define ll long long
using namespace std;int a[MAXN][MAXN];
int b[MAXN];int main(void) {for(int i=1; i<=5; ++i) {for(int j=1; j<=5; ++j) {scanf("%d", &a[i][j]);}b[i] = i;}ll sum = a[b[1]][b[2]] + a[b[2]][b[1]] + a[b[2]][b[3]] + a[b[3]][b[2]] + 2*a[b[3]][b[4]] + 2*a[b[4]][b[3]] + 2*a[b[4]][b[5]]+2*a[b[5]][b[4]];ll bestsum = sum;while(next_permutation(b+1, b+6)) {sum = a[b[1]][b[2]] + a[b[2]][b[1]] + a[b[2]][b[3]] + a[b[3]][b[2]] + 2*a[b[3]][b[4]] + 2*a[b[4]][b[3]] + 2*a[b[4]][b[5]]+2*a[b[5]][b[4]];//  cout << "sum = " << sum << endl;if(sum > bestsum)bestsum = sum;}cout << bestsum << endl;return 0;
}

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