C ++ algorithms: recursive search insertion position ----- variant binary search

topic:

Given a sorted array and a target, find the object in the array, and returns its index. If the target is not present in the array, it will be returned in sequence inserted position. You may assume that no duplicate elements in the array.

Example 1:

Input: [1,3,5,6], 5 outputs: 2

Example 2:

Input: [1,3,5,6], Output 2: 1

Example 3:

Input: [1,3,5,6], 7 Output: 4

Ideas:

Variants of binary search method, there are three cases: a. When begin> End time, show nums is empty, directly ret = 0; II. If (begin == end - 1) || time (begin == end), the normal binary search to the last, need to begin or end determines whether == target, or determines the insertion position; III. Recursive binary search

Code:

class Solution {
public:
    int searchInsert(vector<int>& nums, int target) {
        //思路：变种二分查找法,有三种情况：一。当begin>end时，表明nums为空，则直接ret=0；二。当(begin == end - 1) || (begin == end)时，为正常二分查找到最后，需判断begin或end是否==target，或判断插入位置；三。递归二分查找
        int ret = 0;
        binary_search(nums, target, 0, nums.size()-1, ret);
        
        return ret;
    }
private: 
    void binary_search(vector<int>& nums, int target, int begin, int end, int& ret)
    {
        //终止条件
        if(begin > end)  //nums为kong
        {
            ret = 0;
            return ;
        }
        
        if((begin == end - 1) || (begin == end))
        {
            if(nums[begin] >= target)
                ret = begin;
            else if(nums[end] >= target)
                ret = end;
            else
                ret = end+1;
            return ;
        }
        
        int mid = (begin+end)/2;
        
        if(nums[mid] > target)
            binary_search(nums, target, begin, mid-1, ret);
        else if(nums[mid] < target)
            binary_search(nums, target, mid+1, end, ret);
        else
        {
            ret = mid;
            return ;
        }
    }
};