拓扑排序

Posted 2021-02-06 downrainsun

#include<cstdio>
#include<queue>
#include<cstring>
#include<vector>

using namespace std;
const int maxm = 105;

vector<int> ve[maxm];
int indeg[maxm], n, m, num, a[maxm], x, y;
queue<int> q;

void topsort() {
while(!q.empty())q.pop();
num = 0;
for(int i = 1; i <= n; i++) {
    if(!indeg[i]) q.push(i);
}
while(!q.empty()) {
    int nx = q.front();
    a[num++] = nx;
    q.pop();
    for(int i = 0; i < ve[nx].size(); i++) {
        if(--indeg[ ve[nx][i] ] == 0) q.push(ve[nx][i]);
    }
}
}

int main() {
while(~scanf("%d%d", &n, &m)) {
    if(n == 0 && m  == 0) break;
    memset(indeg, 0, sizeof(indeg));
    memset(a, 0, sizeof(a));
    for(int i = 1; i <= n; i++) {
        ve[i].clear();
    }
    while(m--) {
        scanf("%d%d", &x, &y);
        ve[x].push_back(y);
        indeg[y]++;
    }
    topsort();
    for(int i = 0; i < n; i++) {
        if(i == 0) printf("%d", a[i]);
        else printf(" %d", a[i]);
    }
    printf("
");
}

}

找入度为零的点，然后一个一个存，一般用于很多任务，给出几个优先级， 然后得到总的顺序。

https://vjudge.net/contest/280900#problem/A习题