力扣算法 Java 刷题笔记【数组篇 二分搜索】hot100（一）二分查找、搜索插入位置、在排序数组中查找元素的第一个和最后一个位置 3

文章目录

• 1. 二分查找（简单）
• 2. 搜索插入位置（简单）
• 3. 在排序数组中查 找元素的第一个和最后一个位置（中等）

1. 二分查找（简单）

地址: https://leetcode-cn.com/problems/binary-search/
2022/01/30
做题反思：

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

2. 搜索插入位置（简单）

地址: https://leetcode-cn.com/problems/search-insert-position/
2022/01/30
做题反思：

class Solution {
    public int searchInsert(int[] nums, int target) {
        int left = 0, right = nums.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                right = mid - 1;
            }
            if (nums[mid] < target) {
                left = mid + 1;
            }
            if (nums[mid] > target) {
                right = mid - 1;
            }
        }
        return left;
    }
}

3. 在排序数组中查 找元素的第一个和最后一个位置（中等）

地址: https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/
2022/01/30
做题反思：

class Solution {
    public int[] searchRange(int[] nums, int target) {
        return new int[]{leftSearch(nums, target), rightSearch(nums, target)};
    }

    int leftSearch(int[] nums, int target) {
        int left = 0, right = nums.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                right = mid - 1;
            }
            if (nums[mid] < target) {
                left = mid + 1;
            }
            if (nums[mid] > target) {
                right = mid - 1;
            }
        }
        if (left >= nums.length || nums[left] != target) {
            return -1;
        }
        return left;
    }

    int rightSearch(int[] nums, int target) {
        int left = 0, right = nums.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                left = mid + 1;
            }
            if (nums[mid] < target) {
                left = mid + 1;
            }
            if (nums[mid] > target) {
                right = mid - 1;
            }
        }
        if (right < 0 || nums[right] != target) {
            return -1;
        }
        return right;
    }
}