hdu 1142 最短路 + DP

这题题意好纠结，半天没看懂，后来打完过不了样例，让海峰读题，最后按他的思路打完了，居然在他之前AC，哈哈~

读懂了题目还是挺简单的，首先求出所有点到终点的最短路，然后DP一下，就能求出路径条数。

/*
 * hdu1142/linux.cpp
 * Created on: 2011-9-17
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

const int SIZE = 1005;
const int MAX = 0x7fffffff;

typedef struct {
    int index;
    int pathlen;
    int routes;
} MyPoint;

int N, M;
int map[SIZE][SIZE];
int D[SIZE];
MyPoint mypoints[SIZE];

bool operator<(const MyPoint &p1, const MyPoint &p2) {
    if (p1.pathlen != p2.pathlen) {
        return p1.pathlen > p2.pathlen;
    } else {
        return p1.index < p2.index;
    }
}

void dijistra(int s) {
    int i, j, k, mind, minf;
    int visited[SIZE];
    for (i = 0; i < N; i++) {
        visited[i] = 0;
        D[i] = map[s][i];
    }
    visited[s] = 1;
    D[s] = 0;
    for (i = 1; i < N; i++) {
        mind = MAX;
        minf = MAX;
        k = 0;
        for (j = 0; j < N; j++) {
            if (visited[j]) {
                continue;
            }
            if (D[j] < mind) {
                k = j;
                mind = D[j];
            }
        }
        visited[k] = 1;
        for (j = 0; j < N; j++) {
            if (!visited[j]) {
                if (D[k] < D[j] - map[k][j]) {
                    D[j] = D[k] + map[k][j];
                }
            }
        }
    }
}

void Buildmap() {
    int i, j, k, p;
    for (i = 0; i < N; i++) {
        for (j = 0; j < N; j++) {
            map[i][j] = MAX;
        }
        map[i][i] = 0;
    }
    for (k = 0; k < M; k++) {
        scanf("%d%d%d", &i, &j, &p);
        map[i - 1][j - 1] = p;
        map[j - 1][i - 1] = p;
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    while (scanf("%d", &N) == 1 && N > 0) {
        scanf("%d", &M);
        Buildmap();
        dijistra(1);
        for (int i = 0; i < N; i++) {
            mypoints[i].index = i;
            mypoints[i].pathlen = D[i];
            mypoints[i].routes = 0;
        }
        sort(mypoints, mypoints + N);
        int i = 0;
        while (mypoints[i].index != 0) {
            i++;
        }
        mypoints[i].routes = 1;
        for (; i < N - 1; i++) {
            for (int j = i + 1; j < N; j++) {
                if (mypoints[j].pathlen < mypoints[i].pathlen) {
                    if (map[mypoints[i].index][mypoints[j].index] < MAX) {
                        mypoints[j].routes += mypoints[i].routes;
                    }
                }
            }
        }
        printf("%d\n", mypoints[N - 1].routes);
    }
    return 0;
}