[Algorithm Topic Breakthrough] Binary Search - 704. Binary Search (16)

Table of contents

1. Question analysis

2. Algorithm principle

3. Code writing

Write at the end:

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1. Question analysis

Question link: 704. Binary search - LeetCode

The question is very simple, just find a target. 

2. Algorithm principle

According to the most basic binary search algorithm:

In an ordered array, the left and right boundaries are left and right respectively, and the value of the position pointed by mid is x. 

1. x < target，left  = mid + 1

2. x > target，right = mid - 1

3. x == target, just return the result·

3. Code writing

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

4. The first bisection template

This is our first template~

        while (left <= right) {

            int mid = left + (right - left) / 2;

            if ( ... ) left = mid + 1;

            else if ( ... ) right = mid - 1;

            else if ( ... ) return mid;

        }

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