C语言二分查找

#include <stdio.h>

/*
二分查找条件: 1、有序序列  2、数据在数组中
*/

int baseBinarySearch(int a[],int h,int k)
{
    int low=0;
    int high=h;
    int mid =0;
    int NoFound = -1;
    while (low <= high)
    {
        mid = low + (high-low) /2 ;
        if ( k < a[mid] )
        {
            high = mid - 1;
        }
        else if ( k > a[mid] )
        {
            low = mid + 1;
        }
        else
        {
            return mid;
        }
    }
    return NoFound;
}

//查找第一个相等的元素
int FirstElementBinSearch(int a[],int h,int k)
{
    int low=0;
    int high=h;
    int mid =0;
    int NoFound = -1;
    while (low <= high)
    {
        mid = low + (high-low) /2 ;
        if ( k <= a[mid] )
        {
            high = mid - 1;
        }
        else
        {
            low = mid + 1;
        }
    }
    return low <= h ? low : NoFound;
}

//查找最后一个相等的元素low

int LastElementBinSearch(int a[],int h,int k)
{
    int low=0;
    int high=h;
    int mid =0;
    int NoFound = -1;
    while (low <= high)
    {
        mid = low + (high-low) /2 ;
        if ( k >= a[mid] )
        {
           low = mid + 1 ;
        }
        else
        {
            high = mid -1 ;
        }
    }
    printf("%d %d %d\n",low,high,a[low-1]);

    if (low - 1 >= 0 && a[low - 1] ==k)
    {
        return low-1;
    }
    return NoFound;
}

原文地址：https://www.cnblogs.com/flashBoxer/p/9471527.html