【算法】回溯—排列问题

#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 1000 + 5;
const int inf = 1e9;
int cost[maxn][maxn]; // i j work_i peo_j
int a[maxn];
int n;
int bestC = inf, currC;
void back(int t)
{
    if (t == n)
    {
        bestC = min(bestC, currC);
    }
    //back(t+1)
    for (int i = t; i < n; ++i)
    {
        swap(a[t], a[i]);
        currC += cost[t][a[t]];
        if (currC < bestC)
            back(t + 1);
        currC -= cost[t][a[t]];
        swap(a[t], a[i]);
    }
}
int main()
{
    cin >> n;
    for (int i = 0; i < n; ++i)
        a[i] = i;
    for (int i = 0; i < n; ++i)
        for (int j = 0; j < n; ++j)
            cin >> cost[i][j];
    back(0);
    cout << bestC << endl;
    return 0;
}

~

上界函数还是很有用的，很粗乱的统计如下
（感觉这样统计似乎没什么意义）