四刷41

Author: diguage

docs/0041-first-missing-positive.adoc

@@ -1,7 +1,7 @@
 [#0041-first-missing-positive]
 = 41. 缺失的第一个正数
 
-{leetcode}/problems/first-missing-positive/[LeetCode - First Missing Positive^]
+https://leetcode.cn/problems/first-missing-positive/[LeetCode - 41. 缺失的第一个正数^]
 
 给你一个未排序的整数数组 `nums` ，请你找出其中没有出现的最小的正整数。
 
@@ -42,12 +42,12 @@
 
 == 思路分析
 
-这道题跟 {leetcode}/problems/missing-number/[268. Missing Number - LeetCode^] 很像！
-
-
+这道题跟 xref:0268-missing-number.adoc[268. Missing Number] 很像！
 
 image::images/0041-01.png[{image_attr}]
 
+image::images/0041-10.png[{image_attr}]
+
 [[src-0041]]
 [tabs]
 ====
@@ -77,10 +77,20 @@ include::{sourcedir}/_0041_FirstMissingPositive_2.java[tag=answer]
 include::{sourcedir}/_0041_FirstMissingPositive_3.java[tag=answer]
 ----
 --
+
+四刷::
++
+--
+[{java_src_attr}]
+----
+include::{sourcedir}/_0041_FirstMissingPositive_4.java[tag=answer]
+----
+--
 ====
 
 
 == 参考资料
 
 . https://leetcode.cn/problems/first-missing-positive/solutions/304743/que-shi-de-di-yi-ge-zheng-shu-by-leetcode-solution/[41. 缺失的第一个正数 - 官方题解^]
 . https://leetcode.cn/problems/first-missing-positive/solutions/7703/tong-pai-xu-python-dai-ma-by-liweiwei1419/[41. 缺失的第一个正数 - 原地哈希（哈希函数为：f(nums[i\]) = nums[i\] - 1）^]
+. https://leetcode.cn/problems/first-missing-positive/solutions/3655377/huan-zuo-wei-tong-guo-li-zi-li-jie-suan-qa94e/[41. 缺失的第一个正数 - O(n) 换座位，通过例子理解算法思想^]

docs/images/0041-10.png

@@ -1529,6 +1529,11 @@ endif::[]
 |{doc_base_url}/0215-kth-largest-element-in-an-array.adoc[题解]
 |⭕️ 快速选择。有思路，但代码总报错！还需要多练！
 
+|{counter:codes2503}
+|{leetcode_base_url}/first-missing-positive/[41. 缺失的第一个正数^]
+|{doc_base_url}/0041-first-missing-positive.adoc[题解]
+|✅ 循环排序。
+
 |===
 
 截止目前，本轮练习一共完成 {codes2503} 道题。

logbook/202503.adoc

@@ -0,0 +1,30 @@
+package com.diguage.algo.leetcode;
+
+public class _0041_FirstMissingPositive_4 {
+  // tag::answer[]
+
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-09-14 22:15:15
+   */
+  public int firstMissingPositive(int[] nums) {
+    int length = nums.length;
+    for (int i = 0; i < length; i++) {
+      while (nums[i] > 0 && nums[i] < length && nums[i] != i + 1) {
+        int num = nums[i];
+        if (nums[num - 1] == num) {
+          break;
+        }
+        nums[i] = nums[num - 1];
+        nums[num - 1] = num;
+      }
+    }
+    for (int i = 0; i < length; i++) {
+      if (nums[i] != i + 1) {
+        return i + 1;
+      }
+    }
+    return length + 1;
+  }
+  // end::answer[]
+}

src/main/java/com/diguage/algo/leetcode/_0041_FirstMissingPositive_4.java

@@ -5,7 +5,7 @@ public class _0215_KthLargestElementInAnArray_6 {
 
   /**
    * @author D瓜哥 · https://www.diguage.com
-   * @since 2025-04-30 07:16:18
+   * @since 2025-09-13 22:15:50
    */
   public int findKthLargest(int[] nums, int k) {
     return quickselect(nums, 0, nums.length - 1, nums.length - k);