[LeetCode][JavaScript]Search for a Range

Search for a Range 

Given a sorted array of integers, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

For example,
Given [5, 7, 7, 8, 8, 10] and target value 8,
return [3, 4].

https://leetcode.com/problems/search-for-a-range/

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给定有序的数列，要求找出目标，要求时间复杂度O(logn)，二分法。

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    var len = nums.length, start = 0; end = len - 1;
    while(start <= end){
        var index = parseInt((start + end) / 2);
        if(nums[index] === target){
            start = end = index;
            while(start - 1 >= 0 && nums[start - 1] === target) start--;
            while(end + 1 <= len - 1 && nums[end + 1] === target) end++;
            return [start, end];
        }else if(nums[index] > target){
            end = index - 1;
        }else if(nums[index] <target){
            start = index + 1;
        }
    }
    return [-1, -1];
};