Question
Formatted question description: https://leetcode.ca/all/228.html
228. Summary Ranges
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.
@tag-array
Algorithm
Traverse the array once and check whether the next number is increasing each time
- If yes, continue to traverse down
- If not, we have to judge whether it is a number or a sequence at this time,
- A number is directly stored in the result
- The sequence should be stored in the first and last numbers and the arrow “->”.
We need two variables i and j, where i is the position of the starting number of the continuous sequence, j is the length of the continuous sequence, when j is 1, it means there is only one number, if it is greater than 1, it is a continuous sequence.
Code
Java
import java.util.ArrayList;
import java.util.List;
public class Summary_Ranges {
class Solution {
public List<String> summaryRanges(int[] nums) {
List<String> result = new ArrayList<>();
int left = 0, n = nums.length;
while (left < n) {
int right = 1;
while (left + right < n && (long)nums[left + right] - nums[left] == right) {
++right;
}
result.add(
right <= 1 ?
String.valueOf(nums[left])
: String.valueOf(nums[left]) + "->" + String.valueOf(nums[left + right - 1]));
left += right;
}
return result;
}
}
}