hdu 5348 MZL's endless loop 2015多校联合训练赛#5 找环+dfs

MZL's endless loop

Time Limit: 3000/1500 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 1837    Accepted Submission(s): 395
Special Judge

Problem Description

As we all kown, MZL hates the endless loop deeply, and he commands you to solve this problem to end the loop.
You are given an undirected graph with  n  vertexs and  m  edges. Please direct all the edges so that for every vertex in the graph the inequation  |out degree − in degree|≤1  is satisified.
The graph you are given maybe contains self loops or multiple edges.

 

Input

The first line of the input is a single integer  T , indicating the number of testcases.
For each test case, the first line contains two integers  n  and  m .
And the next  m  lines, each line contains two integers  ui  and  vi , which describe an edge of the graph.
T≤100 ,  1≤n≤105 ,  1≤m≤3∗105 ,  ∑n≤2∗105 ,  ∑m≤7∗105 .

 

Output

For each test case, if there is no solution, print a single line with  −1 , otherwise output  m  lines,.
In  i th line contains a integer  1  or  0 ,  1  for direct the  i th edge to  ui→vi ,  0  for  ui←vi .

 

Sample Input

   
   
   
   

    
    
    
    2
3 3
1 2
2 3
3 1
7 6
1 2
1 3
1 4
1 5
1 6
1 7
   
   
   
   

题目：把无向边变有向边，每个点的出度入度只差小于等于1

：把环找出来，一个环上，每个点的入度=出度

：剩下一片森林，森林里dfs保证每个结点的出度与入度只差相差1即可。一定有答案

http://blog.sina.com.cn/s/blog_15139f1a10102vokk.html 解题报告

#pragma comment(linker, "/STACK:102400000,102400000")
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
struct Node{
    int u,v,id,f;
};
#define maxn 100007
vector<Node>head[maxn];
vector<Node>edge;

int in[maxn],out[maxn],check[maxn*5],result[maxn*5];
int cnt = 0;
vector<Node>stack;
int dfn[maxn];
int olar(int u,int dep){
    Node p,q;
    dfn[u] = dep;
    while(head[u].size() > 0){
        p = head[u][head[u].size()-1];
        head[u].pop_back();

        if(check[p.id]) continue;
        check[p.id] = 1;

        stack.push_back(p);
        if(dfn[p.v] != -1 ) {
            dfn[u] = -1;
            return p.v;
        }

        int v = olar(p.v,dep+1);

        if( v != 0){
            if( v == u){
                for(int i = dep;i < stack.size(); i++){
                    q = stack[i];
                    result[q.id] = q.f;
                }
                while(stack.size() > dep)
                    stack.pop_back();
            }
            else {
                dfn[u] = -1;
                return v;
            }
        }
        else stack.pop_back();
    }
    dfn[u] = -1;
    return 0;
}

void dfs(int u){
    int v;
    Node p;
    while(head[u].size() > 0){
        p = head[u][head[u].size()-1];
        head[u].pop_back();
        if(check[p.id]) continue;

        check[p.id] = 1;

        if(out[u] > in[u]){
            in[u]++;
            out[p.v]++;
            result[p.id] = p.f;
        }
        else {
            out[u]++;
            in[p.v]++;
            result[p.id] = !p.f;
        }
        dfs(p.v);
    }
}

int main(){
    int t,n,m;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);
        for(int i = 1;i <= n; i++)
            in[i] = out[i] = 0, dfn[i] = -1;

        for(int i = 0;i < m; i++)
            check[i] = 0,result[i] = -1;

        Node p;
        edge.clear();
        for(int i = 1;i <= n; i++)
            head[i].clear();

        for(int i = 0;i < m; i++){
            scanf("%d%d",&p.u,&p.v);
            p.f = 1;
            p.id = i;
            edge.push_back(p);
            if(p.u == p.v){
                result[p.id] = 1;
                continue;
            }

            head[p.u].push_back(p);

            swap(p.u,p.v);
            p.f = 0;
            head[p.u].push_back(p);
        }

        for(int i = 1;i <= n; i++)
            if(head[i].size() > 0)
                olar(i,0);
        //cout<<"x"<<endl;
        for(int i = 0;i < m; i++){
            if(result[i] == -1){
                p = edge[i];
                head[p.u].push_back(p);
                swap(p.u,p.v);
                p.f = 0;
                head[p.u].push_back(p);
            }
            check[i] = 0;
        }

        for(int i = 1;i <= n; i++)
            if(head[i].size() > 0) {
                dfs(i);
            }

        int ans = 1;
//cout<<cnt<<endl;
        for(int i = 1;i <= n; i++)
            if(in[i] > out[i] +1 || in[i] + 1 < out[i])
                ans = -1;
        if(ans == -1){
            printf("-1\n");
        }
        else
            for(int i = 0;i < m; i++)
                printf("%d\n",result[i]);
    }
    return 0;
}
/*

55

4 20
1 1
2 2
3 3
4 4
1 2
1 2
1 2
1 2
2 3
2 3
2 3
2 3
3 4
3 4
3 4
3 4
4 1
4 1
4 1
4 1

3 3
1 2
2 3
3 1

7 6
1 2
1 3
1 4
1 5
1 6
1 7
*/