拓扑排序

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

const int maxn = 5e5 + 10;
int N, M;
int h[maxn], v[maxn], in[maxn], nx[maxn];
int  sz = 0;

void init() {
    for(int i = 1; i <= N; i ++) {
        h[i] = -1;
        in[i] = 0;
    }
    sz = 0;
}

void add(int a, int b) {
    v[sz] = b;
    nx[sz] = h[a];
    h[a] = sz;
    in[b] ++;
    sz ++;
}

void TopSort() {
    queue<int> q;
    vector<int> ans;

    for(int i = 1; i <= N; i ++) {
        if(in[i] == 0)
            q.push(i);
    }

    while(!q.empty()) {
        int tp = q.front();
        q.pop();
        ans.push_back(tp);

        for(int i = h[tp]; i != -1; i = nx[i]) {
            in[v[i]] --;
            if(in[v[i]] == 0)
                q.push(v[i]);
        }
    }

    if(ans.size() != N)
        printf("NO\n");
    else {
        for(int i = 0; i < ans.size(); i ++)
            printf("%d%s", ans[i], i != ans.size() - 1 ? " " : "\n");
    }

}

int main() {
    while(~scanf("%d%d", &N, &M)) {
        init();
        for(int i = 0; i < M; i ++) {
            int a, b;
            scanf("%d%d", &a, &b);
            add(a, b);
        }
        TopSort();
    }
    return 0;
}

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