网络流：宇宙旅行C语言代码

以下是一个基于C语言的网络流代码，用于解决宇宙旅行问题：

#include <stdio.h>
#include <string.h>
#include <limits.h>

#define MAX_N 1000
#define INF INT_MAX

int capacity[MAX_N][MAX_N];  // 容量矩阵
int flow[MAX_N][MAX_N];      // 流量矩阵
int parent[MAX_N];           // 父节点数组

int bfs(int source, int sink, int n) {
    int visited[MAX_N] = {0};  // 是否被访问过
    int queue[MAX_N];          // 广度优先搜索队列
    int front = 0, rear = 0;   // 队列头尾指针

    queue[rear++] = source;
    visited[source] = 1;

    while (front < rear) {
        int u = queue[front++];

        for (int v = 0; v < n; v++) {
            if (!visited[v] && capacity[u][v] > flow[u][v]) {
                visited[v] = 1;
                parent[v] = u;
                if (v == sink) {
                    return 1;
                }
                queue[rear++] = v;
            }
        }
    }
    return 0;
}

int max_flow(int source, int sink, int n) {
    int total_flow = 0;

    memset(flow, 0, sizeof(flow));

    while (bfs(source, sink, n)) {
        int path_flow = INF;

        for (int v = sink; v != source; v = parent[v]) {
            int u = parent[v];
            path_flow = path_flow < capacity[u][v] - flow[u][v] ? path_flow : capacity[u][v] - flow[u][v];
        }

        for (int v = sink; v != source; v = parent[v]) {
            int u = parent[v];
            flow[u][v] += path_flow;
            flow[v][u] -= path_flow;
        }

        total_flow += path_flow;
    }

    return total_flow;
}

int main() {
    int n, m, s, t;
    scanf("%d%d%d%d", &n, &m, &s, &t);

    memset(capacity, 0, sizeof(capacity));

    for (int i = 0; i < m; i++) {
        int u, v, w;
        scanf("%d%d%d", &u, &v, &w);
        capacity[u][v] += w;
    }

    printf("%d\n", max_flow(s, t, n));

    return 0;
}

其中，`capacity`表示容量矩阵，`flow`表示流量矩阵，`parent`表示父节点数组。`bfs`函数用于实现广度优先搜索，返回是否能从源点到汇点，`max_flow`函数用于实现最大流算法，返回最大流量。在主函数中，依次输入节点数`n`、边数`m`、源点`s`、汇点`t`和每条边的起始节点、结束节点和容量，最终输出最大流量。