常用算法归集

二分查找

 //递归法
int binary_search(const int arr[], int start, int end, int khey) {
	if (start > end)
		return -1;

	int mid = start + (end - start) / 2;   
	if (arr[mid] > khey)
		return binary_search(arr, start, mid - 1, khey);
	else if (arr[mid] < khey)
		return binary_search(arr, mid + 1, end, khey);
	else
	    return mid;   
}

//while 循环法
int binary_search(const int arr[], int start, int end, int key) {
    int ret = -1;      
    
	int mid;
	while (start <= end) {
		mid = start + (end - start) / 2; 
		if (arr[mid] < key)
			start = mid + 1;
		else if (arr[mid] > key)
			end = mid - 1;
		else {           
			ret = mid;  
            break;
        }
	}
	
	return ret;    
}