58 lines
1007 B
C++
58 lines
1007 B
C++
#include<stdio.h>
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#include<string.h>
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int pre[2][100010];
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int n,m;
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int find(int a,int i)
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{
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int r=a;
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while(r!=pre[i][r])
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{
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r=pre[i][r];
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}
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return r;
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}
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void fun(int a,int b)
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{
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if(a!=n)
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{
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int fa=find(a,0),fb=find(b,0);
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if(fa!=fb)
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pre[0][a]=b;
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}
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if(b!=n)
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{
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int fa=find(a,1),fb=find(b,1);
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if(fa!=fb)
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pre[1][b]=a;
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}
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}
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int main()
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{
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while(scanf("%d%d",&n,&m)!=EOF,n||m)
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{
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int i,w=1;
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for(i=0;i<=n;i++)
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{
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pre[0][i]=pre[1][i]=i;
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}
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while(m--)
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{
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int a,b;
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scanf("%d%d",&a,&b);
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fun(a,b);
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}
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for(i=1;i<=n;i++)
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{
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if(find(i,0)!=n||find(i,1)!=n)
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{
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w=0;
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break;
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}
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}
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if(w)
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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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}
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