邻接表数组实现

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#include<stdio.h>#include<algorithm>#include<string.h>#include<queue>using namespace std;int head[400010];struct node{    int n_v;    int next;}edge[400010];int bfs(int n){    queue<int>q;    int vis[200010];    memset(vis,0,sizeof(vis));    int s = 1,e = n;    int vs;    q.push(1);    vis[1] = 1;    while(!q.empty()){        s = q.front();        q.pop();        for (int t = head[s];t!=-1;t = edge[t].next){            vs = edge[t].n_v;            if(vs == e)return 1;            if(vis[vs] == 0){                q.push(vs);                vis[vs] = 1;            }        }    }    return 0;}int main(){    int n,m;    while(scanf("%d%d",&n,&m)!=EOF){        int u ,v;        int k = 0;        memset(head,-1,sizeof(head));        for (int i = 0;i<m;i++){            scanf("%d%d",&u,&v);            edge[k].n_v = v;            edge[k].next = head[u];            head[u] = k++;            edge[k].n_v = u;            edge[k].next = head[v];            head[v] = k++;        }        if(bfs(n))puts("POSSIBLE");        else puts("IMPOSSIBLE");    }}

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