HDU5418.Victor and World（状压DP）

 

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <algorithm>

using namespace std;

typedef long long ll;
const int INF = 0x5f5f5f5f;
const int MAX = 1 << 17;

int mp[20][20];
int dp[MAX + 1][20];    // dp[s][v] 走过s点，现在在v点 dp[S][0]

int bit[1<<17];

int main()
{
    //freopen("in.txt", "r", stdin);

	for(int i = 0; i<(1<<16); i++) // bit[i] := i的二进制有多少个1
    {
        bit[i] = 0;
        for (int j = 0; j <= 16; j++)
            if (i & (1 << j))
              bit[i]++;
    }

    int t;
    int m, n;
    scanf("%d", &t);
    while (t--) {
        memset(mp, -1, sizeof mp);
        for (int i = 0; i < MAX; ++i)
            for (int j = 0; j < 16; ++j)
                dp[i][j] = INF;

        scanf("%d%d", &n, &m);
        int a, b, c;
        for (int i = 0; i < m; ++i) {
            scanf("%d%d%d", &a, &b, &c);
            if (mp[a - 1][b - 1] == -1 || mp[a - 1][b - 1] > c)
                mp[a - 1][b - 1] = mp[b - 1][a - 1] = c;
        }

        int maxn =  (1 << n) - 1;

		dp[1][0] = 0;
        for (int s = 1; s <= maxn; ++s) {
			for(int k = 0; k <= bit[s]; ++k) {
				for (int v = 0; v < n; ++v) {
					if (dp[s][v] != INF) {
						for (int u = 0; u < n; ++u) {
							if (mp[u][v] != -1) {
								if (dp[s | (1 << u)][u] > dp[s][v] + mp[u][v])
									dp[s | (1 << u)][u] = dp[s][v] + mp[u][v];
							}
						}
					}
				}
            }
        }

        printf("%d\n", dp[maxn][0]);
    }

    return 0;
}

/**
Input:
2
3 2
1 2 2
1 3 3
5 4
1 2 1
2 3 1
3 4 1
4 5 1

Output:
10
8
*/

　　

wa了好久，我只想知道

for(int k = 0; k <= bit[s]; ++k) 

什么意思，为什么要加这句？