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56. Merge Intervals Leetcode Javascript Solution

The Problem:

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.

Example 1:

Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].

Example 2:

Input: intervals = [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.

Constraints:

  • 1 <= intervals.length <= 104
  • intervals[i].length == 2
  • 0 <= starti <= endi <= 104

The Problem:

var merge = function(intervals) {
    if(intervals.length == 1 || intervals.length == 0){ return intervals}
    intervals.sort((a,b) => a[0] !== b[0] ? a[0]-b[0] : a[1]-b[1])
   // console.log(intervals)
    let ans = [], prev = intervals[0]
    ans.push(prev)
    for(let interval of intervals){
       // console.log(prev)
        if(interval[0] <= prev[1]){
            prev[1] = Math.max(interval[1], prev[1])
            //prev = interval (remember not to update prev in this if
        } else {
            ans.push(interval)
            prev = interval
        }
       // console.log(ans)
    }
    return ans
};
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41. First Missing Positive Leetcode Javascript Solution

The Problem:

Given an unsorted integer array nums, find the smallest missing positive integer.

Example 1:

Input: nums = [1,2,0]
Output: 3

Example 2:

Input: nums = [3,4,-1,1]
Output: 2

Example 3:

Input: nums = [7,8,9,11,12]
Output: 1

Constraints:

  • 0 <= nums.length <= 300
  • -231 <= nums[i] <= 231 - 1

The Solution:

var firstMissingPositive = function(nums) {
    if(nums.length == 0) return 1
    let ans = 999999, changed = false
    nums.sort((a,b) => a-b)
    if(nums[0] > 1  || nums[nums.length-1] < 0){
        return 1
    }
   //console.log(nums)
    for(let i = 0; i < nums.length-1; i++){
        if(nums[i] >= 0){
            let diff = nums[i+1] - nums[i]
            //console.log(diff)
            if( diff > 1){
                ans = Math.min(ans, nums[i] + 1)
                //console.log("max " + ans)
                changed =true
            }
        } else {
              if(nums[i +1] > 1 && nums[i] < 0){
               return 1
           }
        }
    }
    if(changed == false){
        ans = nums[nums.length-1] + 1
    }
    return ans
};