Summary Ranges LeetCode Solution | Easy Approach

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Summary Ranges You are given a sorted unique integer array nums.

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.

Summary Ranges Solutions

Time: O(n)
Space: O(n)

C++

class Solution {
 public:
  vector<string> summaryRanges(vector<int>& nums) {
    vector<string> ans;

    for (int i = 0; i < nums.size(); ++i) {
      const int begin = nums[i];
      while (i + 1 < nums.size() && nums[i] == nums[i + 1] - 1)
        ++i;
      const int end = nums[i];
      if (begin == end)
        ans.push_back(to_string(begin));
      else
        ans.push_back(to_string(begin) + "->" + to_string(end));
    }

    return ans;
  }
};

Java

 class Solution {
  public List<String> summaryRanges(int[] nums) {
    List<String> ans = new ArrayList<>();

    for (int i = 0; i < nums.length; ++i) {
      final int begin = nums[i];
      while (i + 1 < nums.length && nums[i] == nums[i + 1] - 1)
        ++i;
      final int end = nums[i];
      if (begin == end)
        ans.add("" + begin);
      else
        ans.add("" + begin + "->" + end);
    }

    return ans;
  }
}

Python

  class Solution:
  def summaryRanges(self, nums: List[int]) -> List[str]:
    ans = []

    i = 0
    while i < len(nums):
      begin = nums[i]
      while i < len(nums) - 1 and nums[i] == nums[i + 1] - 1:
        i += 1
      end = nums[i]
      if begin == end:
        ans.append(str(begin))
      else:
        ans.append(str(begin) + "->" + str(end))
      i += 1

    return ans

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