HDU - 1385 Minimum Transport Cost(最短路＋最小字典序路径)

题目大意：有N个村庄。过村庄时需要交一定的费用。现在问从村庄A，要运一批货物到村庄B，怎样走才能使费用达到最小，起始和终点都不用缴费

解题思路：这题借鉴了别人的思路，用字符串存储路径。

其实不用字符串也是可以处理的

[code]#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;
#define N 105
#define INF 0x3f3f3f3f

struct Node {
    char str
;
    int dis;
    int len;
}node
;

int dis

, tax
, d
, start, End, n;
bool vis
;

void init() {
    int x, y;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            scanf("%d", &x);
            dis[i][j] = x;
            if (x == -1 || i == j)
                dis[i][j] = INF;
        }
    }

    for (int i = 1; i <= n; i++)
        scanf("%d", &tax[i]);
}

void SPFA() {
    memset(vis, 0, sizeof(vis));
    for (int i = 1; i <= n; i++) {
        d[i] = INF;
        node[i].len = 0;
    }

    node[start].str[0] = start;
    node[start].len = 1;

    d[start] = 0;
    vis[start] = true;
    queue<int> q;
    q.push(start);

    while (!q.empty()) {
        int t = q.front();
        q.pop();
        vis[t] = 0;

        for (int i = 1; i <= n; i++) {
            if (i != t) { //还没有走到终点,且最短距离变更
                int tt = d[t] + dis[t][i];
                if (i != End)
                    tt += tax[i];
                bool mark = false;
                if (tt <= d[i]) {
                    //如果最短距离小于上一次的最短距离，直接更新
                    if (tt < d[i]) {
                        d[i] = tt;
                        mark = true;
                    }
                    else {
                        //最短距离相等的，查看字典序是否最小
                        int len = min(node[i].len, node[t].len);
                        //flag == 1表示上一个的字典序比较小，flag == 2表示当前的字典需比较小，flag == 0表示在长度相同的情况下，字典序相同
                        int flag = 0;
                        for (int j = 0; j < len; j++) {
                            if (node[i].str[j] < node[t].str[j]) {
                                flag = 1;
                                break;
                            }
                            if (node[i].str[j] > node[t].str[j]) {
                                flag = 2;
                                break;
                            }
                        }
                        //当前的字典序比上一个小
                        if (flag == 2) {
                            mark = true;
                        }
                        else if(flag == 0) {
                            //如果在长度相同的情况下字典序还相同,那么上一个字典序，那么只可能是上一个的长度比当前的长
                            if (node[i].len > node[t].len) {
                                if (node[i].str[node[t].len] > i) 
                                    mark = true;
                            }
                        }
                    }
                }
                if (mark) {
                    for (int j = 0; j < node[t].len; j++)
                        node[i].str[j] = node[t].str[j];

                    node[i].str[node[t].len] = i;
                    node[i].len = node[t].len + 1;
                    if (!vis[i]) {
                        vis[i] = 1;
                        q.push(i);
                    }
                }
            }
        }
    }
    node[End].str[node[End].len] = '\0';
    printf("From %d to %d :\n", start, End);
    printf("Path: %d", start);
    for (int i = 1; i < node[End].len; i++)
        printf("-->%d", node[End].str[i]);
    printf("\n");
    printf("Total cost : %d\n\n", d[End]);
}

void solve() {
    while (1) {
        scanf("%d%d", &start, &End);
        if (start == -1 && End == -1)
            break;
        SPFA();
    }
}

int main() {
    while (scanf("%d", &n) != EOF && n) {
        init();
        solve();
    }
    return 0;
}