五刷15

Author: diguage

docs/0015-3sum.adoc

@@ -1,7 +1,7 @@
 [#0015-3sum]
 = 15. 三数之和
 
-https://leetcode.cn/problems/3sum/[LeetCode - 15. 三数之和 ^]
+https://leetcode.cn/problems/3sum/[LeetCode - 15. 三数之和^]
 
 给你一个整数数组 `nums` ，判断是否存在三元组 `[nums[i], nums[j], nums[k]]` 满足 `i != j`、`i != k` 且 `j != k` ，同时还满足 `nums[i] + nums[j] + nums[k] == 0`。请你返回所有和为 `0` 且不重复的三元组。
 
@@ -92,6 +92,15 @@ include::{sourcedir}/_0015_3Sum_3.java[tag=answer]
 include::{sourcedir}/_0015_3Sum_4.java[tag=answer]
 ----
 --
+
+五刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0015_3Sum_5.java[tag=answer]
+----
+--
 ====
 
 == 参考资料

logbook/202503.adoc

@@ -1499,6 +1499,11 @@ endif::[]
 |{doc_base_url}/0056-merge-intervals.adoc[题解]
 |✅ 复习 {doc_base_url}/0000-04-merge-intervals.adoc[Merge Intervals 区间合并]。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。
 
+|{counter:codes2503}
+|{leetcode_base_url}/3sum/[15. 三数之和^]
+|{doc_base_url}/0015-3sum.adoc[题解]
+|✅ 复习 {doc_base_url}/0000-06-two-pointer.adoc[Two Pointer 双指针]。双指针+递归降维。
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

src/main/java/com/diguage/algo/leetcode/_0015_3Sum_5.java

@@ -0,0 +1,72 @@
+package com.diguage.algo.leetcode;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class _0015_3Sum_5 {
+  // tag::answer[]
+
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2018-07-15 00:58
+   */
+  public List<List<Integer>> threeSum(int[] nums) {
+    Arrays.sort(nums);
+    return numSum(nums, 0, 3, 0);
+  }
+
+  private List<List<Integer>> numSum(int[] nums, int index, int count, int target) {
+    if (index + count > nums.length || count < 2) {
+      return new ArrayList<>();
+    }
+    if (count == 2) {
+      int left = index, right = nums.length - 1;
+      List<List<Integer>> result = new ArrayList<>();
+      while (left < right) {
+        int ln = nums[left], rn = nums[right];
+        if (target < ln) {
+          break;
+        }
+        int sum = ln + rn;
+        if (sum == target) {
+          result.add(new ArrayList<>(List.of(ln, rn)));
+          while (left < right && nums[left] == ln) {
+            left++;
+          }
+          while (left < right && nums[right] == rn) {
+            right--;
+          }
+        } else if (target < sum) {
+          while (left < right && nums[right] == rn) {
+            right--;
+          }
+        } else {
+          while (left < right && nums[left] == ln) {
+            left++;
+          }
+        }
+      }
+      return result;
+    } else {
+      List<List<Integer>> result = new ArrayList<>();
+      while (index + count <= nums.length) {
+        int sn = nums[index];
+        List<List<Integer>> temp = numSum(nums, index + 1, count - 1, target - sn);
+        for (List<Integer> l : temp) {
+          l.add(sn);
+          result.add(l);
+        }
+        while (index + count <= nums.length && nums[index] == sn) {
+          index++;
+        }
+      }
+      return result;
+    }
+  }
+
+  // end::answer[]
+  public static void main(String[] args) {
+    new _0015_3Sum_5().threeSum(new int[]{0, 0, 0});
+  }
+}

src/main/java/com/diguage/algo/leetcode/_0017_LetterCombinationsOfAPhoneNumber.java

@@ -40,7 +40,10 @@
  */
 public class _0017_LetterCombinationsOfAPhoneNumber {
   // tag::answer[]
-
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2019-07-19 00:19
+   */
   private List<String> result = new ArrayList<>();
   public List<String> letterCombinations(String digits) {
     if (Objects.isNull(digits) || digits.length() == 0) {

src/main/java/com/diguage/algo/leetcode/_0018_4Sum.java

@@ -37,6 +37,9 @@ public class _0018_4Sum {
      * Runtime: 4 ms, faster than 94.46% of Java online submissions for 4Sum.
      *
      * Memory Usage: 40.7 MB, less than 52.17% of Java online submissions for 4Sum.
+     *
+     * @author D瓜哥 · https://www.diguage.com
+     * @since 2018-07-15 00:58
      */
     public List<List<Integer>> fourSum(int[] nums, int target) {
         int numCount = 4;