广度优先搜索

#include <bits/stdc++.h>
#define N 10001
using namespace std;

int n, m;
int head[N], sumedge;
bool vis[N];

struct Edge {
    int x, y, z, next;
    Edge(int x = 0, int y = 0, int z = 0, int next = 0) :
        x(x), y(y), z(z), next(next) {}
} edge[N * 2];

void ins(int x, int y, int z) {
    edge[++sumedge] = Edge(x, y, z, head[x]);
    head[x] = sumedge;
    return;
}

void bfs() {
    queue<int> q;
    vis[1] = 1;
    q.push(1);
    while (q.size()) {
        int t = q.front();
        printf("%d ", t);
        q.pop();
        for (int u = head[t]; u; u = edge[u].next) {
            if (!vis[edge[u].y] && edge[u].z != 0) {
                vis[edge[u].y] = 1;
                q.push(edge[u].y);
            }
        }
    }
}

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        ins(x, y, 1);
    }
    bfs();
}