# LC 228. Summary Ranges

### [Problem link](https://leetcode.com/problems/summary-ranges/)

###### tags: `leedcode` `python` `easy` `Two Pointer`

You are given a **sorted unique** integer array <code>nums</code>.

A **range** <code>[a,b]</code> is the set of all integers from <code>a</code> to <code>b</code> (inclusive).

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

Each range <code>[a,b]</code> in the list should be output as:

- <code>"a->b"</code> if <code>a != b</code>
- <code>"a"</code> if <code>a == b</code>

**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:**

- <code>0 <= nums.length <= 20</code>
- <code>-2³¹ <= nums[i] <= 2³¹ - 1</code>
- All the values of <code>nums</code> are **unique** .
- <code>nums</code> is sorted in ascending order.

## Solution 1 - Two pointer

class Solution:
    def summaryRanges(self, nums: List[int]) -> List[str]:
        res = []
        n = len(nums)
        left, right = 0, 0

        while right < n:
            if right + 1 >= n or nums[right] + 1 != nums[right + 1]:
                if left != right:
                    res.append(f"{nums[left]}->{nums[right]}")
                else:
                    res.append(str(nums[left]))
                left = right + 1

            right += 1

        return res

>### Complexity
>| | Time Complexity | Space Complexity |
>| ----------- | --------------- | ---------------- |
>| Solution 1 | O(n) | O(n) |

## Note
x