DFS

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

#define N 100010

int n, m;
int h[N], cnt;
int stack[N], top;
bool inStack[N];
int count[N];
bool ring;

struct edge{
    int to;
    int next;
}E[N];

void add(int v, int w){
    E[++cnt].next = h[v];
    E[cnt].to = w;
    h[v] = cnt;
}

void topo_dfs(int x){
    for(int i = h[x]; i != -1; i = E[i].next){
        int j = E[i].to;
        if(inStack[j]) continue;
        count[j] = count[x] + 1;
        if(count[j] >= n){
            ring = true;
            return;
        }
        topo_dfs(j);
    }
    stack[++top] = x;
    inStack[x] = true; 
}

int main(){

    scanf("%d %d", &n, &m);
    memset(h, -1, sizeof h);

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

    if(ring) printf("-1");
    else {
        for (int x = 1; x <= n; x++)
            if (!inStack[x])   topo_dfs(x);

        if(top == n)   for(int i = top; i >= 1; i--) printf("%d ", stack[i]);
        else printf("-1");
    }

    return 0;
}

BFS

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

#define N 100010

int n, m;
int h[N], cnt;
int d[N];
int que[N], head, tail;

struct edge{
    int to;
    int next;
}E[N];

void add(int v, int w){
    E[++cnt].next = h[v];
    E[cnt].to = w;
    h[v] = cnt;
}

bool topological(){
    for(int i = 1; i <= n; i++)
        if(d[i] == 0)
            que[++tail] = i;

    while(head != tail){
        int t = que[++head];

        for(int i = h[t]; i != -1; i = E[i].next){
            int j = E[i].to;
            if(--d[j] == 0)
                que[++tail] = j;
        }
    }

    return tail == n;
}

int main(){

    scanf("%d %d", &n, &m);
    memset(h, -1, sizeof h);

    for(int i = 1; i <= m; i++){
        int x, y;
        scanf("%d %d", &x, &y);
        add(x, y);
        d[y]++;
    }

    if(topological()){
        for(int i = 1; i <= n; i++) printf("%d ", que[i]);
    }
    else printf("-1");

    return 0;
}

还有个与BFS算法思想类似，维护一个栈的kahn算法