[JS] Find First and Last Position of Element in Sorted Array

🔒 문제 (LeetCode 34)

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

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

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

Constraints:

• 0 <= nums.length <= 105
• -109 <= nums[i] <= 109
• nums is a non-decreasing array.
• -109 <= target <= 109

 

🌊 입출력

Example 1:

Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]

Example 2:

Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]

Example 3:

Input: nums = [], target = 0
Output: [-1,-1]

 

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🔑 해결

🌌 알고리즘 - 이분탐색

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let result = [];
    let l = 0;
    let r = nums.length - 1;
    
    while(l < r) {
        let mid = l + r >>> 1;
        
        if(nums[mid] < target) {
            l = mid + 1;
        } else r = mid;
    }
    
    if(nums[r] !== target) return [-1, -1];
    else result.push(r);
    
    while(nums[r] === target) r++;
    result.push(r-1);
    
    return result;
};