228. Summary Ranges
Description
You are given a sorted unique integer array nums
.
A range [a,b]
is the set of all integers from a
to b
(inclusive).
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"
ifa != b
"a"
ifa == 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.
Solutions
Solution 1: Two Pointers
We can use two pointers $i$ and $j$ to find the left and right endpoints of each interval.
Traverse the array, when $j + 1 < n$ and $nums[j + 1] = nums[j] + 1$, move $j$ to the right, otherwise the interval $[i, j]$ has been found, add it to the answer, then move $i$ to the position of $j + 1$, and continue to find the next interval.
Time complexity $O(n)$, where $n$ is the length of the array. Space complexity $O(1)$.
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