uva 10763交換學生(快速檢索，二分檢索)

P89

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm> using namespace std;struct AB{int a,b,sum;}bz[500005];int cmp(AB x,AB y){return x.a<y.a;}int OK(int key,int end){int left=0,right=end,mid;while(left<right){mid=(left+right)/2;if(bz[key].b<bz[mid].a) right=mid-1;else if(bz[key].b>bz[mid].a) left=mid+1;else right=mid;}if(bz[key].b!=bz[right].a) return 0;else {while(bz[key].b==bz[right].a){if(bz[key].a==bz[right].b&&bz[key].sum==1&&bz[right].sum==1){bz[key].sum=2; bz[right].sum=2;return 1;}else right++;}return 0;}} int main(int argc, char *argv[]){int n,i,j,a,b,t;while(scanf("%d",&n)==1&&n){   for(i=0;i<n;i++){scanf("%d%d",&bz[i].a,&bz[i].b);bz[i].sum=1;}sort(bz,bz+n,cmp);t=0;for(i=1;i<n;i++)if(OK(i,n-1)) t++; if(t*2==n) cout<<"YES"<<endl;else cout<<"NO"<<endl;}return 0;}