LeetCode 228. Summary Ranges

原题链接在这里：https://leetcode.com/problems/summary-ranges/

题目：

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.

题解：

start is starting element, when nums[i] is not cut from nums[i - 1], we need to add a range [start, nums[i - 1]].

Note: Don't forget to add the last range. [start, nums[n - 1].

Time Complexity: O(nums.length).

Space:O(1), regardless res.

AC Java:

class Solution {
    public List<String> summaryRanges(int[] nums) {
        List<String> res = new ArrayList<>();
        if(nums == null || nums.length == 0){
            return res;
        }
        
        int n = nums.length;
        int start = nums[0];
        for(int i = 1; i<n; i++){
            if(nums[i] != nums[i - 1] && nums[i - 1] + 1 != nums[i]){
                res.add(getRange(start, nums[i - 1]));
                start = nums[i];
            }
        }
        
        res.add(getRange(start, nums[n - 1]));
        
        return res;
    }
    
    private String getRange(int l, int r){
        return l == r ? "" + l : l + "->" + r;
    }
}

类似Missing Ranges, Data Stream as Disjoint Intervals.