LeetCode - Easy - 228. Summary Ranges
Topic Array Two Pointers
Description
https://leetcode.com/problems/summary-ranges/
You are given a sorted unique integer array
Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of
Each range
Example 1:
Example 2:
Example 3:
Example 4:
Example 5:
Constraints: 0 <= nums.length <= 20 -2³¹ <= nums[i] <= 2³¹ - 1 All the values of
Analysis
略
Submission
Test
Description
https://leetcode.com/problems/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"
Example 3:
Input: nums = []
Output: []
Example 4:
Input: nums = [-1]
Output: ["-1"]
Example 5:
Input: nums = [0]
Output: ["0"]
Constraints:
nums
are unique. nums
is sorted in ascending order. Analysis
略
Submission
public class SummaryRanges {
// :
public List<String> summaryRanges1(int[] nums) {
List<String> result = new ArrayList<>();
if (nums == null || nums.length == 0)
return result;
int left = nums[0], right = nums[0];
for (int i = 1; i < nums.length; i++) {
if (right + 1 == nums[i]) {
right++;
} else {
result.add(left == right ? left + "" : left + "->" + right);
left = right = nums[i];
}
}
result.add(left == right ? left + "" : left + "->" + right);
return result;
}
// : ,
public List<String> summaryRanges2(int[] nums) {
List<String> list = new ArrayList<>();
for (int i = 0; i < nums.length; i++) {
int a = nums[i];
while (i + 1 < nums.length && nums[i + 1] - nums[i] == 1)
i++;
list.add(a == nums[i] ? a + "" : a + "->" + nums[i]);
}
return list;
}
}
Test
import static org.junit.Assert.*;
import org.hamcrest.collection.IsEmptyCollection;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.collection.IsIterableContainingInOrder.contains;
import org.junit.Test;
public class SummaryRangesTest {
@Test
public void test() {
SummaryRanges obj = new SummaryRanges();
assertThat(obj.summaryRanges1(new int[] {
0, 1, 2, 4, 5, 7}), //
contains("0->2", "4->5", "7"));
assertThat(obj.summaryRanges1(new int[] {
0, 2, 3, 4, 6, 8, 9}), //
contains("0","2->4","6","8->9"));
assertThat(obj.summaryRanges1(new int[] {
}), IsEmptyCollection.empty());
assertThat(obj.summaryRanges1(new int[] {
-1}), contains("-1"));
assertThat(obj.summaryRanges1(new int[] {
0}), contains("0"));
assertThat(obj.summaryRanges2(new int[] {
0, 1, 2, 4, 5, 7}), //
contains("0->2", "4->5", "7"));
assertThat(obj.summaryRanges2(new int[] {
0, 2, 3, 4, 6, 8, 9}), //
contains("0","2->4","6","8->9"));
assertThat(obj.summaryRanges2(new int[] {
}), IsEmptyCollection.empty());
assertThat(obj.summaryRanges2(new int[] {
-1}), contains("-1"));
assertThat(obj.summaryRanges2(new int[] {
0}), contains("0"));
}
}