C语言->二分查找

方法1: 循环

#define  _CRT_SECURE_NO_WARNINGS
#include "stdio.h"
#include "stdlib.h"

int binarySearch(int *arr, int findNum,int length)
{
	int head = 0;
	int back = length - 1;
	while (head <= back) {
		int mid = (head + back) / 2;
		if (arr[mid] < findNum)
		{
			head = mid + 1;
		}
		else if(arr[mid] > findNum) 
		{
			back = mid - 1;
		}
		else
		{
			return mid;
		}
	}
	return -1;


}


void main()
{
	int data[] = { 1, 3, 6, 7, 9, 12, 14, 16, 17, 18, 20, 21, 22, 23, 30, 32, 33, 35 };
	int length = sizeof(data) / sizeof(int);
	int findABC = binarySearch(data, 35,length);
	if(findABC != -1)
	{
		printf("找到了!!!元素ID为%d, 元素为%d", findABC,data[findABC]);
	}
	else
	{
		printf("没找到啊!");
	}
	system("pause");
}

方法2:递归

int * binarySearchStack(int *arr, int findNum, int length)
{
    int* head = arr;
    int* back = arr + length - 1;
    int* mid = arr + (length - 1) / 2;
    if ((back - head) >= 0)
    {
        if (*mid == findNum)
        {
            printf("找到了");
            return mid;
        }
        else if (*mid < findNum)
        {
            binarySearchStack(mid +1, findNum, back - mid);
        }
        else
        {
            binarySearchStack(arr, findNum, mid - head);
        }
    }
    else
    {
        printf("找不到");
        return NULL;
    }


}
void main()
{
    int data[] = { 1, 3, 6, 7, 9, 12, 14, 16, 17, 18, 20, 21, 22, 23, 30, 32, 33, 35 };
    int length = sizeof(data) / sizeof(int);
    int* findABC = binarySearchStack(data, 99, length);
    if (findABC != NULL)
    {
        printf("找到了!!!元素ID为%d, 元素为%d", findABC-data, *findABC);
    }
    else
    {
        printf("没找到啊!");
    }
    system("pause");
}