hdu 5215 判断奇偶环

来源：互联网发布：百度学术知乎编辑：程序博客网时间：2024/06/13 18:10
#include <cstdio>#include <iostream>#include <algorithm>#include <queue>#include <cmath>#include <cstring>#include <stack>#include <set>#include <map>#include <vector>using namespace std;#define INF 0x2fffffff#define LL long long#define MAX(a,b) ((a)>(b))?(a):(b)#define MIN(a,b) ((a)<(b))?(a):(b)#pragma comment(linker, "/STACK:102400000,102400000") int n,m;struct node{    int from,to,next;};node es[600010];int head[100005];int cnt = 0;void add(int from,int to){    es[cnt].from = from,es[cnt].to = to;    es[cnt].next = head[from];    head[from] = cnt++;}int color[100005];int tag[100005];int pre[100005];int flag1,flag2;void dfs(int u){    for(int v = head[u]; v!=-1;v = es[v].next){        node& g = es[v];        if(g.to == pre[u]) continue;        if(!color[g.to]){            color[g.to] = 3 - color[g.from];            pre[g.to] = g.from;            dfs(g.to);            if(flag1&&flag2){                break;            }        }        else{            if(color[g.to] == color[g.from]){                flag1 = 1;                int q = g.from;                while(pre[q] != g.to){                    if(tag[q]) {                        flag2 = 1;                        break;;                    }                     tag[q] = 1;                    q = pre[q];                    if(q == -1) break;                }            }            else{                flag2 = 1;            }        }    }           }int main(){    int t;    cin >> t;    while(t--){        scanf("%d%d",&n,&m);        memset(head,-1,sizeof(head));        cnt = 0;        for(int i = 0;i < m;i++){            int x,y;            scanf("%d%d",&x,&y);            add(x,y),add(y,x);        }        memset(color,0,sizeof(color));        memset(tag,0,sizeof(tag));        memset(pre,-1,sizeof(pre));        flag1 = 0;        flag2 = 0;        for(int i = 1;i <= n;i++){            if(!color[i]){                color[i] = 1;                dfs(i);                if(flag1 && flag2){                    break;                }            }        }        if(flag1){            printf("YES\n");        }        else{            printf("NO\n");        }        if(flag2){            printf("YES\n");        }        else{            printf("NO\n");        }    }    return 0;}
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