From 50595343bd15e783948cca226609f13cad22d7ed Mon Sep 17 00:00:00 2001
From: Hiro Funatsuka <hiro.funatsuka@gmail.com>
Date: Sat, 9 May 2026 22:57:59 +0900
Subject: [PATCH] Solve longest increasing subsequence

---
 300_longest_increasing_subsequence/problem.md |  1 +
 300_longest_increasing_subsequence/step1.md   | 27 +++++++++++++++++++
 300_longest_increasing_subsequence/step2.md   | 19 +++++++++++++
 300_longest_increasing_subsequence/step3.md   | 21 +++++++++++++++
 4 files changed, 68 insertions(+)
 create mode 100644 300_longest_increasing_subsequence/problem.md
 create mode 100644 300_longest_increasing_subsequence/step1.md
 create mode 100644 300_longest_increasing_subsequence/step2.md
 create mode 100644 300_longest_increasing_subsequence/step3.md

diff --git a/300_longest_increasing_subsequence/problem.md b/300_longest_increasing_subsequence/problem.md
new file mode 100644
index 0000000..d182746
--- /dev/null
+++ b/300_longest_increasing_subsequence/problem.md
@@ -0,0 +1 @@
+## 問題: [300. Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/description/)
diff --git a/300_longest_increasing_subsequence/step1.md b/300_longest_increasing_subsequence/step1.md
new file mode 100644
index 0000000..1e36f15
--- /dev/null
+++ b/300_longest_increasing_subsequence/step1.md
@@ -0,0 +1,27 @@
+# Step 1
+
+- 漸化式を作れなかった
+- [NeetCode](https://www.youtube.com/watch?v=cjWnW0hdF1Y)の解法を見た
+  - LIS[i] を「nums[i] から始まる最長増加部分列の長さ」と定義する
+  - 各要素単体でも部分列なので、初期値をすべて 1 にする
+  - 後ろから順に各 index i を処理する
+  - i より右側の要素 j を見て、nums[i] < nums[j] なら連結可能
+  - 連結できる場合、LIS[i] = max(LIS[i], 1 + LIS[j]) で更新する
+  - 最後に LIS 配列の最大値を返す
+
+```python
+class Solution:
+    def lengthOfLIS(self, nums: List[int]) -> int:
+        LIS = [1] * len(nums)
+
+        for i in range(len(nums) - 1, -1, -1):
+            for j in range(len(nums) - 1, i, -1):
+                if nums[i] < nums[j]:
+                    LIS[i] = max(LIS[i], 1 + LIS[j])
+
+        return max(LIS)
+```
+
+時間計算量: $O(n^2)$
+
+空間計算量: $O(n)$
diff --git a/300_longest_increasing_subsequence/step2.md b/300_longest_increasing_subsequence/step2.md
new file mode 100644
index 0000000..4747d2b
--- /dev/null
+++ b/300_longest_increasing_subsequence/step2.md
@@ -0,0 +1,19 @@
+# Step 2
+
+```python
+class Solution:
+    def lengthOfLIS(self, nums: List[int]) -> int:
+        lis_from_i = [1] * len(nums)
+
+        for i in range(len(nums) - 1, -1, -1):
+            for j in range(len(nums) - 1, i, -1):
+                if nums[i] < nums[j]:
+                    lis_from_i[i] = max(lis_from_i[i], 1 + lis_from_i[j])
+
+        return max(lis_from_i)
+
+```
+
+時間計算量: $O(n^2)$
+
+空間計算量: $O(n)$
diff --git a/300_longest_increasing_subsequence/step3.md b/300_longest_increasing_subsequence/step3.md
new file mode 100644
index 0000000..e8f35aa
--- /dev/null
+++ b/300_longest_increasing_subsequence/step3.md
@@ -0,0 +1,21 @@
+# Step 3
+
+```python
+class Solution:
+    def lengthOfLIS(self, nums: List[int]) -> int:
+        lis_from_i = [1] * len(nums)
+
+        for i in range(len(nums) - 1, -1, -1):
+            for j in range(len(nums) - 1, i, -1):
+                if nums[i] < nums[j]:
+                    lis_from_i[i] = max(lis_from_i[i], 1 + lis_from_i[j])
+
+        return max(lis_from_i)
+
+```
+
+1回目: 1分　17秒
+
+2回目: 1分　23秒
+
+3回目: 1分　14秒