Bellman-Ford算法：POJ No.3169 Layout 差分约束

#define _CRT_SECURE_NO_WARNINGS
/*
4 2 1
1 3 10 2 4 20
2 3 3
*/
#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
using namespace std;

const int maxn = 10000 + 200;
const int INF = 999999;
//输入
int N, ML, MD;
int AL[maxn], BL[maxn], DL[maxn];
int AD[maxn], BD[maxn], DD[maxn];

int d[maxn];

void solve()
{
    fill(d, d + N, INF);
    d[0] = 0;

    //用Bellman-Ford算法计算d
    for (int k = 0; k < N; k++) {
        //从i+1到i的权值为0
        for (int i = 0; i + 1 < N; i++) {
            if (d[i + 1] < INF) d[i] = min(d[i], d[i + 1]);
        }
        //从AL到BL的权值为DL
        for (int i = 0; i < ML; i++) {
            if (d[AL[i] - 1] < INF) {
                d[BL[i] - 1] = min(d[BL[i] - 1], d[AL[i] - 1] + DL[i]);
            }
        }
        //从BD到AD的权值为-DD
        for (int i = 0; i < MD; i++) {
            if (d[BD[i] - 1] < INF) {
                d[AD[i] - 1] = min(d[AD[i] - 1], d[BD[i] - 1] - DD[i]);
            }
        }
    }
    int res = d[N - 1];
    if (d[0] < 0) {
        //存在负边无解
        res = -1;
    }
    else if (res == INF) {
        res = -2;
    }
    printf("%d
", res);
}

void input()
{
    cin >> N >> ML >> MD;
    for (int i = 0; i < ML; i++) {
        cin >> AL[i] >> BL[i] >> DL[i];
    }
    for (int i = 0; i < MD; i++) {
        cin >> AD[i] >> BD[i] >> DD[i];
    }
}

int main()
{
    input();
    solve();
    return 0;
}