二刷56

Author: diguage

docs/0056-merge-intervals.adoc

@@ -1,35 +1,61 @@
 [#0056-merge-intervals]
-= 56. Merge Intervals
+= 56. 合并区间
 
-{leetcode}/problems/merge-intervals/[LeetCode - Merge Intervals^]
+https://leetcode.cn/problems/merge-intervals/[LeetCode - 56. 合并区间 ^]
 
-Given a collection of intervals, merge all overlapping intervals.
+以数组 `intervals` 表示若干个区间的集合，其中单个区间为 `+intervals[i] = [start+`~`+i+`~`+, end+`~`+i+`~`+]+`。请你合并所有重叠的区间，并返回 _一个不重叠的区间数组，该数组需恰好覆盖输入中的所有区间_ 。
 
-*Example 1:*
 
-[subs="verbatim,quotes,macros"]
-----
-*Input:* [[1,3],[2,6],[8,10],[15,18]]
-*Output:* [[1,6],[8,10],[15,18]]
-*Explanation:* Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].
+*示例 1：*
 
-----
+....
+输入：intervals = [[1,3],[2,6],[8,10],[15,18]]
+输出：[[1,6],[8,10],[15,18]]
+解释：区间 [1,3] 和 [2,6] 重叠, 将它们合并为 [1,6].
+....
 
-*Example 2:*
+*示例 2：*
+
+....
+输入：intervals = [[1,4],[4,5]]
+输出：[[1,5]]
+解释：区间 [1,4] 和 [4,5] 可被视为重叠区间。
+....
+
+
+*提示：*
+
+* `+1 <= intervals.length <= 10+`^`+4+`^
+* `+intervals[i].length == 2+`
+* `+0 <= start+`~`+i+`~`+<= end+`~`+i+`~`+<= 10+`^`+4+`^
 
-[subs="verbatim,quotes,macros"]
-----
-*Input:* [[1,4],[4,5]]
-*Output:* [[1,5]]
-*Explanation:* Intervals [1,4] and [4,5] are considered overlapping.
-----
 
-*NOTE:* input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.
+
+== 思路分析
 
 
 [[src-0056]]
+[tabs]
+====
+一刷::
++
+--
 [{java_src_attr}]
 ----
 include::{sourcedir}/_0056_MergeIntervals.java[tag=answer]
 ----
+--
+
+二刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0056_MergeIntervals_2.java[tag=answer]
+----
+--
+====
+
+
+== 参考资料
 

logbook/202503.adoc

@@ -25,6 +25,11 @@ endif::[]
 |{doc_base_url}/0033-search-in-rotated-sorted-array.adoc[题解]
 |⭕️ 重点去处理有序部分，在有序部分内查找不到，则去另外一部分去查找。
 
+|{counter:codes2503}
+|{leetcode_base_url}/merge-intervals/[56. Merge Intervals^]
+|{doc_base_url}/0056-merge-intervals.adoc[题解]
+|✅ 对区间进行排序，然后快慢指针在当前数组上对其进行合并。
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

src/main/java/com/diguage/algo/leetcode/_0056_MergeIntervals_2.java

@@ -0,0 +1,35 @@
+package com.diguage.algo.leetcode;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+public class _0056_MergeIntervals_2 {
+  // tag::answer[]
+
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-03-05 17:14:39
+   */
+  public int[][] merge(int[][] intervals) {
+    // 对待合并区间进行排序，首先按照起点排序，然后按终点排序
+    // 排序后，可以保证起点有序；在起点相等时，终点有序。
+    Arrays.sort(intervals, Comparator.comparingInt((int[] o) -> o[0])
+      .thenComparingInt(o -> o[1]));
+    int merged = 0, curr = 0;
+    while (merged < intervals.length && curr < intervals.length) {
+      if (intervals[curr][0] <= intervals[merged][1]) {
+        // 如果当前区间起点小于等于合并后区间的终点，那么直接合并到已经合并的区间里
+        intervals[merged][1] = Math.max(intervals[merged][1], intervals[curr][1]);
+      } else {
+        // 如果当前区间起点大于合并后区间的终点，那么直接开启新的合并区间
+        merged++;
+        intervals[merged] = intervals[curr];
+      }
+      // 每次合并，当前区间都要向前走一下。
+      curr++;
+    }
+    return Arrays.copyOf(intervals, merged + 1);
+  }
+
+  // end::answer[]
+}