57 lines
1.0 KiB
C++
57 lines
1.0 KiB
C++
#include<iostream>
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#include<vector>
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#include<stack>
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#include<stdio.h>
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using namespace std;
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vector<int> V[1010];
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stack<int> S;
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int N;
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int dfs(int v,int pre) //涓寮
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{
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int i,t;
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int sum=0;
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for(i=0;i<V[v].size();i++)
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{
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t=V[v][i];
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if(t!=pre)
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sum=sum^(dfs(t,v)+1);
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}
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return sum;
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}
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int main()
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{
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int i,flag,t;
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while(scanf("%d",&N)!=EOF)
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{
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for(i=0;i<=N;i++)
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V[i].clear();
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while(!S.empty())
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S.pop();
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for(i=0;i<N;i++)
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{
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scanf("%d",&t);
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if(t!=-1)
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{
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V[t].push_back(i);
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V[i].push_back(t);
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}
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else
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{
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S.push(i);
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}
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}
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int t,sum=0;
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while(!S.empty())
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{
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t=S.top();
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S.pop();
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sum=sum^dfs(t,-1);
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}
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if(sum)
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printf("YES\n");
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else
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printf("NO\n");
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}
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return 0;
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}
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