228. Summary Ranges

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LeetCode

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Problem

Given a sorted integer array without duplicates, return the summary of its ranges.

Example 1:

Input:  [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: 0,1,2 form a continuous range; 4,5 form a continuous range.

Example 2:

Input:  [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: 2,3,4 form a continuous range; 8,9 form a continuous range.

Code

class Solution {
    public List<String> summaryRanges(int[] nums) {
        List<String> res = new ArrayList<>();
        if(nums == null || nums.length == 0) return res;

        for(int i = 0; i < nums.length; i++){
            int num = nums[i];
            while(i < nums.length - 1 && nums[i] + 1 == nums[i + 1]){
                i++;
            }

            // 是一个范围
            if(num != nums[i]){
                res.add(num + "->" + nums[i]);
            // 是一个数字
            } else {
                res.add(num + "");
            }
        }

        return res;
    }
}

class Solution:
    def summaryRanges(self, nums: List[int]) -> List[str]:
        if not nums:
            return []

        res = []
        start = nums[0]

        for i in range(1, len(nums)):
            if  nums[i] == nums[i - 1] + 1:
                continue

            if  start == nums[i - 1]:
                res.append(str(start))
            else:
                res.append(str(start) + "->" + str(nums[i - 1]))

            start = nums[i]

        if nums[-1] == start:
            res.append(str(nums[-1]))
        else:
            res.append(str(start) + "->" + str(nums[-1]))

        return res