二分查找求上界 下界

#include<stdio.h>

#include<time.h>

#include<stdlib.h>

int a[10]={5,5,2,6,5,8,3,8,5,9};

int hig_binSearch(int n,int b,int e){//左闭右开

while(e-b>1){ //有一个元素

int m = b+(e-b)/2;

if(n<=a[m]) b=m;

else e=m;

}

if(a[b]==n) return b+1;

else return -1;

}

int low_binSearch(int n,int b,int e){

while(e-b>1){

int m = b+(e-b)/2;

if(n>a[m]) b=m+1; //n在右边

else if(n==a[m]) e=m+1; //左边可能有小的

else e=m; //n在左边

}

printf("%d %d\n",b,e);

if(a[b]==n) return b+1;

else return -1;

}

void qsort(int b,int e){

printf("%d %d\n",b,e);

if(e-b>1){ //一个元素的跳过

int x=b,y=e;

while(x<y){

while(x+1<e&&a[++x]<=a[b]);

while(y-1>=b&&a[--y]>=a[b]);

if(x<y){int t=a[x];

a[x]=a[y];

a[y]=t;

}

}

int t=a[b];a[b]=a[y];a[y]=t;

for(int i=0;i<10;i++) printf("%d ",a[i]);

printf("\n");

qsort(b,y);

qsort(y+1,e);

}

}

int main(){

qsort(0,10);

for(int i=0;i<10;i++) printf("%d ",a[i]);

printf("\n");

int l=low_binSearch(5,0,10);

if(l==-1) printf("not found\n");

else printf("%d\n",l);

return 0;

}