二分查找

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算法要求在五行之内写出二分查找，我用了6行，不知道有高手可以用五行写出来不：

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#include<stdio.h>

#include<stdlib.h>

int a[]={10,22,42,51,56,63,78,99,102,118};

int binary_search(int low, int high, int key) {

if(low > high)

return -1;

int mid = low + (high - low) / 2;

if(a[mid] == key)

return mid;

return (a[mid] > key ? binary_search(low, mid-1, key) : binary_search(mid+1, high, key));

}

void main() {

int result = binary_search(0, sizeof(a)/sizeof(int), 102);

printf("%d\n",a[result]);

}

注意 int mid = low + (high - low) / 2;这句，很多面试题目都有这个问题，这个主要是编程的细节问题，开始可能想到这样写：int mid = (low + high) / 2;但是 low，和high的值加起来之后有可能超出int的表示范围，从而使其成为负数。

==============评论里有人写:

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int binSearch(int* a, int begin, int end, int k){

int mid = begin + ( (end - begin)>>1 ),index;

index = a[mid] < k && begin + 1 < end ? binSearch(a,mid+1,end,k) :

( a[mid] > k && begin + 1 < end ? binSearch(a,begin,mid,k) :

mid * (a[mid] == k) + (a[mid] != k)*(-1));

return index;

}