leetcode34在排序数组查找元素第一和最后位置

题目地址

https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/

题目描述

给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。如果数组中不存在目标值 target，返回 [-1, -1]。

进阶：你可以设计并实现时间复杂度为 O(log n) 的算法解决此问题吗？

示例 1：
输入：nums = [5,7,7,8,8,10], target = 8
输出：[3,4]

示例 2：
输入：nums = [5,7,7,8,8,10], target = 6
输出：[-1,-1]

示例 3：
输入：nums = [], target = 0
输出：[-1,-1]

提示：
    0 <= nums.length <= 105
    -109 <= nums[i] <= 109
    nums 是一个非递减数组
    -109 <= target <= 109
```    

## 代码实现
```  
javascript
/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let len = nums.length, left = 0, right = len - 1;
    let start = -1, end = -1;
    while (left <= right) {
        let mid = Math.floor((left + right)/2);
        if (nums[mid] === target) {
            start = mid;
            end = mid;
            while(--start >= 0 && nums[start] === target) {
                
            }
            start++;
            while(++end < len && nums[end] === target) {
                
            }
            end--;
            return [start, end];
        }else if (nums[mid] < target) {
            left = mid + 1;
        }else {
            right = mid - 1;
        }
    }
    return [start, end];
};

代码优化

var searchRange = function(nums, target) {
    let right = nums.length - 1, left = 0;
    // 定义获得最左边目标值的函数
    function getLeft(left, right) {
        while (left <= right) {
            let mid = Math.floor((left + right)/2);
            if (nums[mid] === target) {
                right = mid - 1;
            }else if (nums[mid] < target) {
                left = mid + 1;
            }else {
                right = mid - 1;
            }
        }
        if (left >= nums.length || nums[left] !== target) return -1;
        return left;
    }
    // 定义获得最右边目标值的函数
    function getRight(left, right) {
        while (left <= right) {
            let mid = Math.floor((left + right)/2);
            if (nums[mid] === target) {
                left = mid + 1;
            }else if (nums[mid] < target) {
                left = mid + 1;
            }else {
                right = mid - 1;
            }
        }
        if (right < 0 || nums[right] !== target) return -1;
        return right;
    }
    
    return [getLeft(left,right), getRight(left, right)];
};