Leetcode 704 · binary search

leetcode 704· Two points search

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Title Description
Given a n The elements are ordered （ Ascending ） integer array nums And a target value target , Write a function search nums Medium target, If the target value has a return subscript , Otherwise return to -1.

Answer 1

Assuming that this array is a fully closed array, it is necessary to judge left==right The situation of

be left and right The value of should be +1

class Solution {
    
public:
    int search(vector<int>& nums, int target) {
    
        int left,right,mid;
        left=0,right=nums.size()-1;
        while (left <= right)
        {
    
            mid=(left+right)/2;
            if(nums[mid] == target){
    
                return mid;
            }
            else if(nums[mid] < target){
    
                left=mid+1;
            }
            else {
    
                right=mid-1;
            }
        }
        return -1;
        
    }
};

Explanation 2

Assuming that the interval range is a semi open and semi closed interval, then left and right There can be no equality , The cyclic condition can only be left<right

And the subscript movement of the open interval should not be reduced by one

class Solution {
    
public:
    int search(vector<int>& nums, int target) {
    
        int left,right,mid;
        left=0,right=nums.size();
        while (left < right)
        {
    
            mid=(left+right)/2;
            if(nums[mid] == target){
    
                return mid;
            }
            else if(nums[mid] < target){
    
                left=mid+1;
            }
            else {
    
                right=mid;
            }
        }
        return -1;
        
    }
};