二分查找（折半查找）

一 代码

#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
bool BinarySearch(int * array, int aSize, int key){
    if (array == NULL || aSize == 0) {
        return false;
    }

    int low = 0;
    int mid = 0;
    int high = aSize - 1;
    
    while(low <= high) {
        mid = (low + high) / 2;
        if (key > array[mid]) {
            low = mid + 1;
        } else if (key < array[mid]) {
            high = mid - 1;
        } else {
            std::cout << "exist, index = " << mid << std::endl;
            return true;
        }
    }

    std::cout << "does not exist" << std::endl;
    return false;
}

int main()
{
    std::cout << "hello,world" <<std::endl;
    
    int array[5] = {1, 3, 5, 7, 9};
    bool ret = BinarySearch(array, 5, 7);
    std::cout << ret << std::endl;

    ret = BinarySearch(array, 5, 4);
    std::cout << ret << std::endl;

	return 0;
}

hello,world
exist, index = 3
1
does not exist
0
请按任意键继续. . .

二 算法原理

前提：有序数组，取出最左low，最右边界high。在whilie循环中，对比查找key和居中值array[mid]的大小，即可确定key的存在范围。在范围内进行查找即可。