1. 经典的二分查找:

/*
   num：待查找数组
   [begin, end] ：查找区间
   keyValue：待查找关键字
*/
int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] == keyValue)return mid;
        else if(keyValue > num[mid])begin = mid + 1;
        else end = mid - 1;
    }
    return -1;
}

2.查找第一个与keyValue相等的元素:

int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid, preBegin = begin;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] == keyValue){
            if(begin == preBegin || num[begin - 1] != keyValue)return mid;//看是否是最左边的一个
            end = mid - 1;//如果不是继续缩小区间
        }else if(num[mid] > keyValue){
            end = mid - 1;
        }else{
            begin = mid + 1;
        }
    }
    return -1;
}

3.查找最后一个与keyValue相等的元素:

using namespace std; 
int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid, preEnd = end;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] == keyValue){
            if(mid == preEnd || num[mid + 1] != keyValue)return mid;
            begin = mid + 1;
        }else if(num[mid] > keyValue){
            end = mid - 1;
        }else{
            begin = mid + 1;
        }   
    }
    return -1;
}

4.查找第一个等于或者大于keyValue的元素:

int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid, preBegin = begin;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] >= keyValue){
            if(mid == preBegin || num[mid - 1] < keyValue)return mid;
            end = mid - 1;
        }else{
            begin = mid + 1;
        }
    }
    return -1;
}

5.查找第一个大于keyValue的运算:

int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid, preBegin = begin;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] > keyValue){
            if(mid == preBegin || num[mid - 1] <= keyValue)return mid;
            end = mid - 1;
        }else{
            begin = mid + 1; 
        }
    }
    return -1;
}

6.查找最后一个小于keyValue的元素:

int binaraySearch(int* num , int begin, int end, int keyValue){
    int mid, preEnd = end;
    while(begin <= end){
        mid = begin + (end - begin) / 2;
        if(num[mid] < keyValue){
            if(mid == preEnd || num[mid + 1] >= keyValue)return mid;
            begin = mid + 1;
        }else{
            end = mid - 1;
        }
    }
    return -1;
}

核心思想：

当找到某种情况，要看是否是需要的，如果不是，则继续缩小范围

如果错误，希望各位在下面指出！！ daversun