51 lines
1.4 KiB
C++
51 lines
1.4 KiB
C++
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#include <bits/stdc++.h>
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using namespace std;
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const int N = 5005; //种类上限
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const int M = 500005; //关系数上限
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int n; //种类
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int m; //关系数
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vector<int> edge[N]; //保存DAG图的邻接表
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queue<int> q; //广搜的队列
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int ind[N]; //入度
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/**
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* 测试用例：
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3 3
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1 2
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2 3
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1 3
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输出拓扑排序,注意拓扑排序不是唯一的
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1 2 3
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* @return
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*/
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int main() {
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cin >> n >> m;
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//m种关系
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for (int i = 1; i <= m; i++) {
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int x, y;
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cin >> x >> y;
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ind[y]++; //点y的入度+1
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edge[x].push_back(y); //用邻接表记录下
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}
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//找到所有入度为0的点，放入广度优先搜索的队列
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for (int i = 1; i <= n; i++) if (!ind[i]) q.push(i);
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//广度优先搜索DAG，就是拓扑排序的模板
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while (!q.empty()) {
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int x = q.front();
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q.pop();
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//输出拓扑序
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cout << x << " ";
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for (int i = 0; i < edge[x].size(); i++) { //遍历所有出边
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int y = edge[x][i]; //目标结点
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//对接点入度-1，抹去这条入边
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ind[y]--;
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//如果入度为0，则入队列，准备处理它
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if (!ind[y]) q.push(y);
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}
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}
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return 0;
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}
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