228. Summary Ranges

Problem

You are given a sorted unique integer array nums.

A range [a,b] is the set of all integers from a to b (inclusive).

Return **the *smallest sorted* list of ranges that cover all the numbers in the array exactly**. That is, each element of nums is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums.

Each range [a,b] in the list should be output as:

• "a->b" if a != b

• "a" if a == b

  Example 1:

Input: nums = [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: The ranges are:
[0,2] --> "0->2"
[4,5] --> "4->5"
[7,7] --> "7"

Example 2:

Input: nums = [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: The ranges are:
[0,0] --> "0"
[2,4] --> "2->4"
[6,6] --> "6"
[8,9] --> "8->9"

  Constraints:

• 0 <= nums.length <= 20

• -231 <= nums[i] <= 231 - 1

• All the values of nums are unique.

• nums is sorted in ascending order.

Solution

/**
 * @param {number[]} nums
 * @return {string[]}
 */
var summaryRanges = function(nums) {
    var res = [];
    for (var i = 0; i < nums.length; i++) {
        if (i === 0 || nums[i] !== nums[i - 1] + 1) res.push(`${nums[i]}`);
        else if (i === nums.length - 1 || nums[i] !== nums[i + 1] - 1) res[res.length - 1] += `->${nums[i]}`;
    }
    return res;
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).