数组——二分查找

题目顺序：代码随想录算法公开课，b站上有相应视频讲解

一、题目

704. Binary Search

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4
Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Constraints:

1 <= nums.length <= 104
-104 < nums[i], target < 104
All the integers in nums are unique.
nums is sorted in ascending order.

题目来源：leetcode

二、题解

左闭右闭写法

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

左闭右开写法

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