198. House Robber

198_house_robber/problem.md

@@ -0,0 +1 @@
+## 問題: [198. House Robber](https://leetcode.com/problems/house-robber/description/)

198_house_robber/step1.md

@@ -0,0 +1,25 @@
+# Step 1
+
+- $house(n)$まで訪れた時の最大の額$maxAmount(n)$は、$max(house(n) + maxAmount(n-2), maxAmount(n-1))$である
+
+```python
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        # 問題の制約でnumsのサイズが１以上は保証されているので、0は考慮しない
+        if len(nums) == 1:
+            return nums[0]
+        if len(nums) == 2:
+            return max(nums[0], nums[1])
+        max_amount_prev_2 = nums[0]
+        max_amount_prev_1 = max(nums[0], nums[1])
+        for i in range(2, len(nums)):
+            max_amount = max(max_amount_prev_1, nums[i] + max_amount_prev_2)
+            max_amount_prev_2 = max_amount_prev_1
+            max_amount_prev_1 = max_amount
+        return max_amount_prev_1
+
+```
+
+時間計算量: $O(n)$
+
+空間計算量: $O(1)$

198_house_robber/step2.md

@@ -0,0 +1,23 @@
+# Step 2
+
+```python
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        # 問題の制約でnumsのサイズが１以上は保証されているので、0は考慮しない
+        if len(nums) == 1:
+            return nums[0]
+        if len(nums) == 2:
+            return max(nums[0], nums[1])
+        max_amount_prev_2 = nums[0]
+        max_amount_prev_1 = max(nums[0], nums[1])
+        for i in range(2, len(nums)):
+            max_amount = max(max_amount_prev_1, nums[i] + max_amount_prev_2)
+            max_amount_prev_2 = max_amount_prev_1
+            max_amount_prev_1 = max_amount
+        return max_amount_prev_1
+
+```
+
+時間計算量: $O(n)$
+
+空間計算量: $O(1)$

198_house_robber/step3.md

@@ -0,0 +1,24 @@
+# Step 3
+
+```python
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        if len(nums) == 1:
+            return nums[0]
+        if len(nums) == 2:
+            return max(nums[0], nums[1])
+        max_amount_prev_2 = nums[0]
+        max_amount_prev_1 = max(nums[0], nums[1])
+
+        for i in range(2, len(nums)):
+            max_amount = max(max_amount_prev_1, nums[i] + max_amount_prev_2)
+            max_amount_prev_2 = max_amount_prev_1
+            max_amount_prev_1 = max_amount
+        return max_amount_prev_1
+```
+
+1回目: 1分　46秒
+
+2回目: 1分　58秒
+
+3回目: 1分　47秒