一刷377

Author: diguage

README.adoc

@@ -2665,12 +2665,12 @@ TIP: **公众号的微信号是: `jikerizhi`**。__因为众所周知的原因
 |Medium
 |
 
-//|{counter:codes}
-//|{leetcode_base_url}/combination-sum-iv/[377. Combination Sum IV^]
-//|{source_base_url}/_0377_CombinationSumIV.java[Java]
-//|{doc_base_url}/0377-combination-sum-iv.adoc[题解]
-//|Medium
-//|
+|{counter:codes}
+|{leetcode_base_url}/combination-sum-iv/[377. Combination Sum IV^]
+|{source_base_url}/_0377_CombinationSumIV.java[Java]
+|{doc_base_url}/0377-combination-sum-iv.adoc[题解]
+|Medium
+|
 
 |{counter:codes}
 |{leetcode_base_url}/kth-smallest-element-in-a-sorted-matrix/[378. Kth Smallest Element in a Sorted Matrix^]

docs/0000-26-dp-2-unbounded-knapsack.adoc

@@ -5,6 +5,7 @@
 == 经典题目
 
 . xref:0322-coin-change.adoc[322. Coin Change]
+. xref:0377-combination-sum-iv.adoc[377. Combination Sum IV]
 . xref:0518-coin-change-ii.adoc[518. Coin Change 2]
 . xref:1449-form-largest-integer-with-digits-that-add-up-to-target.adoc[1449. Form Largest Integer With Digits That Add up to Target]
 . xref:1547-minimum-cost-to-cut-a-stick.adoc[1547. Minimum Cost to Cut a Stick]

docs/0377-combination-sum-iv.adoc

@@ -1,54 +1,78 @@
 [#0377-combination-sum-iv]
-= 377. Combination Sum IV
+= 377. 组合总和 Ⅳ
 
-{leetcode}/problems/combination-sum-iv/[LeetCode - Combination Sum IV^]
+https://leetcode.cn/problems/combination-sum-iv/[LeetCode - 377. 组合总和 Ⅳ ^]
 
-Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.
+给你一个由 *不同* 整数组成的数组 `nums` ，和一个目标整数 `target`。请你从 `nums` 中找出并返回总和为 `target` 的元素组合的个数。
 
-*Example:*
+题目数据保证答案符合 32 位整数范围。
 
-[subs="verbatim,quotes,macros"]
-----
-_*nums*_ = [1, 2, 3]
-_*target*_ = 4
+*示例 1：*
 
-The possible combination ways are:
+....
+输入：nums = [1,2,3], target = 4
+输出：7
+解释：
+所有可能的组合为：
 (1, 1, 1, 1)
 (1, 1, 2)
 (1, 2, 1)
 (1, 3)
 (2, 1, 1)
 (2, 2)
 (3, 1)
+请注意，顺序不同的序列被视作不同的组合。
+....
 
-Note that different sequences are counted as different combinations.
-
-Therefore the output is _*7*_.
-----
-
- 
-
-*Follow up:*
+*示例 2：*
 
+....
+输入：nums = [9], target = 3
+输出：0
+....
 
-What if negative numbers are allowed in the given array?
 
+*提示：*
 
-How does it change the problem?
+* `+1 <= nums.length <= 200+`
+* `+1 <= nums[i] <= 1000+`
+* `nums` 中的所有元素 *互不相同*
+* `+1 <= target <= 1000+`
 
+**进阶：**如果给定的数组中含有负数会发生什么？问题会产生何种变化？如果允许负数出现，需要向题目中添加哪些限制条件？
 
-What limitation we need to add to the question to allow negative numbers?
-
-*Credits:*
-
-
-Special thanks to <a href="https://leetcode.com/pbrother/">@pbrother</a> for adding this problem and creating all test cases.
 
+== 思路分析
 
+起初，我以为是深度优先遍历或者回溯。要去验证的时候，发现，这是组合问题，没办法加备忘录。看答案，竟然是 xref:0000-26-dp-2-unbounded-knapsack.adoc[完全背包问题]。
 
 [[src-0377]]
+[tabs]
+====
+一刷::
++
+--
 [{java_src_attr}]
 ----
-include::{sourcedir}/_0377_CombinationSumIV.java[tag=answer]
+include::{sourcedir}/_0377_CombinationSumIv.java[tag=answer]
 ----
-
+--
+
+// 二刷::
+// +
+// --
+// [{java_src_attr}]
+// ----
+// include::{sourcedir}/_0377_CombinationSumIv_2.java[tag=answer]
+// ----
+// --
+====
+
+
+== 参考资料
+
+. https://oi-wiki.org/dp/knapsack/[背包 DP - OI Wiki^]
+. https://leetcode.cn/problems/combination-sum-iv/solutions/124393/xi-wang-yong-yi-chong-gui-lu-gao-ding-bei-bao-wen-/[377. 组合总和 Ⅳ - 希望用一种规律搞定背包问题^]
+. https://leetcode.cn/problems/combination-sum-iv/solutions/740651/gong-shui-san-xie-yu-wan-quan-bei-bao-we-x0kn/[377. 组合总和 Ⅳ - 【宫水三叶】本题与「完全背包」问题的主要区别，以及「溢出处理」说明^]
+. https://leetcode.cn/problems/combination-sum-iv/solutions/740877/fu-xue-ming-zhu-cong-ji-yi-hua-di-gui-tu-rqwy/[377. 组合总和 Ⅳ - 【负雪明烛】从「记忆化递归」推导「动态规划」]
+. https://leetcode.cn/problems/combination-sum-iv/solutions/2706336/ben-zhi-shi-pa-lou-ti-cong-ji-yi-hua-sou-y52j/[377. 组合总和 Ⅳ - 本质是爬楼梯：记忆化搜索 / 递推^]

docs/index.adoc

@@ -839,7 +839,7 @@ include::0374-guess-number-higher-or-lower.adoc[leveloffset=+1]
 
 include::0376-wiggle-subsequence.adoc[leveloffset=+1]
 
-// include::0377-combination-sum-iv.adoc[leveloffset=+1]
+include::0377-combination-sum-iv.adoc[leveloffset=+1]
 
 include::0378-kth-smallest-element-in-a-sorted-matrix.adoc[leveloffset=+1]
 

logbook/202503.adoc

@@ -1244,6 +1244,11 @@ endif::[]
 |{doc_base_url}/0376-wiggle-subsequence.adoc[题解]
 |❌ 贪心算法。一脸懵逼，看答案才懂。
 
+|{counter:codes2503}
+|{leetcode_base_url}/combination-sum-iv/[377. 组合总和 Ⅳ^]
+|{doc_base_url}/0377-combination-sum-iv.adoc[题解]
+|❌ 动态规划 - 完全背包问题。起初以为是回溯，没想到是完全背包问题。
+
 
 |===
 

src/main/java/com/diguage/algo/leetcode/_0377_CombinationSumIv.java

@@ -0,0 +1,25 @@
+package com.diguage.algo.leetcode;
+
+public class _0377_CombinationSumIv {
+  // tag::answer[]
+  /**
+   * @author D瓜哥 · https://www.diguage.com
+   * @since 2025-07-26 22:19:09
+   */
+  public int combinationSum4(int[] nums, int target) {
+    int[] dp = new int[target + 1];
+    dp[0] = 1;
+    for (int i = 1; i <= target; i++) {
+      for (int j = 0; j < nums.length; j++) {
+        if (i >= nums[j]) {
+          dp[i] += dp[i - nums[j]];
+        }
+      }
+    }
+    return dp[target];
+  }
+  // end::answer[]
+  public static void main(String[] args) {
+    new _0377_CombinationSumIv().combinationSum4(new int[]{1, 2, 3}, 4);
+  }
+}