【HDOJ】1619 Unidirectional TSP

题目本身一点儿都不难，但是就是被字典序搞死了。写的挺麻烦，但是过了，逆向做好做一点儿。

/* 1619 */
#include <cstdio>
#include <cstring>
#include <cstdlib>

#define MAXN 15
#define MAXM 105
#define INF    9999999

int dp[MAXN][MAXM];
int path[MAXN][MAXM];
int map[MAXN][MAXM];
int stack[MAXM], top;
int d[3];
int ans;
int n, m;

void solve(int beg) {
    int i, j, k, tmp;

    for (i=0; i<n; ++i)
        dp[i][m-1] = INF;
    dp[beg][m-1] = map[beg][m-1];
    path[beg][m-1] = -1;

    for (j=m-2; j>=0; --j) {
        for (i=0; i<n; ++i) {
            if (i == 0)
                d[0] = n - 1;
            else
                d[0] = i - 1;
            d[1] = i;
            if (i == n-1)
                d[2] = 0;
            else
                d[2] = i + 1;
            if (dp[d[0]][j+1] == dp[d[1]][j+1]) {
                k = d[0]<d[1] ? d[0]:d[1];
                if (dp[k][j+1] == dp[d[2]][j+1])
                    k = k<d[2] ? k:d[2];
                else if (dp[k][j+1] < dp[d[2]][j+1])
                    k = k;
                else
                    k = d[2];
            } else if (dp[d[0]][j+1] < dp[d[1]][j+1]) {
                if (dp[d[0]][j+1] == dp[d[2]][j+1])
                    k = d[0]<d[2] ? d[0]:d[2];
                else if (dp[d[0]][j+1] < dp[d[2]][j+1])
                    k = d[0];
                else
                    k = d[2];
            } else {
                if (dp[d[1]][j+1] == dp[d[2]][j+1])
                    k = d[1]<d[2] ? d[1]:d[2];
                else if (dp[d[1]][j+1] < dp[d[2]][j+1])
                    k = d[1];
                else
                    k = d[2];
            }
            path[i][j] = k;
            dp[i][j] = dp[k][j+1];
            if (dp[i][j] != INF)
                dp[i][j] += map[i][j];
        }
    }

    tmp = INF;
    for (i=0; i<n; ++i) {
        if (dp[i][0] < tmp) {
            tmp = dp[i][0];
            k = i;
        }
    }

    if (tmp < ans) {
        ans = tmp;
        top = 0;
        j = 0;
        stack[top++] = k + 1;
        while (path[k][j] >= 0) {
            stack[top++] = path[k][j] + 1;
            k = path[k][j];
            ++j;
        }
    }
}

int main() {
    int i, j, k, tmp;

    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif

    while (scanf("%d %d", &n, &m) != EOF) {
        for (i=0; i<n; ++i)
            for (j=0; j<m; ++j)
                scanf("%d", &map[i][j]);
        ans = INF;
        for (i=0; i<n; ++i)
            solve(i);

        for (i=0; i<m-1; ++i)
            printf("%d ", stack[i]);
        printf("%d
", stack[m-1]);
        printf("%d
", ans);
    }

    return 0;
}