198. House Robber

198/step1.cpp

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+// Solve Time: 10:49
+//
+// Space Complexity: O(n)
+// Time Complexity: O(n)
+
+/*
+
+なんとなく方針をを決めてそのまま実装する
+配列を用意して、特定の位置における最大利益、とする。
+同日に隣接する箇所は襲えないので、前日の値をそのまま持ってくるか、一昨日の利益に当日の利益を足すか、のどちらかを選ぶ。
+
+benefit += maximumBenefit[i - 2];
+とすべき箇所を
+benefit += nums[i - 2];
+としてしまった
+
+*/
+
+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        vector<int> maximumBenefit(nums.size(), 0);
+        if (nums.size() == 1) {
+            return nums[0];
+        }
+        maximumBenefit[0] = nums[0];
+        for (int i = 1; i < nums.size(); ++i) {
+            int benefit = nums[i];
+            if (i >= 2) {
+                benefit += maximumBenefit[i - 2];
+            }
+            maximumBenefit[i] = max(benefit, maximumBenefit[i - 1]);
+        }
+        return maximumBenefit.back();
+    }
+};

198/step2.cpp

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+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        vector<int> maximumBenefit(nums.size(), 0);
+        maximumBenefit[0] = nums[0];
+        for (int i = 1; i < maximumBenefit.size(); ++i) {
+            int benefit = nums[i];
+            if (i >= 2) {
+                benefit += maximumBenefit[i - 2];
+            }
+            maximumBenefit[i] = max(benefit, maximumBenefit[i - 1]);
+        }
+        return maximumBenefit.back();
+    }
+};

198/step2_2.cpp

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+// 2変数で行う手法
+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        if (nums.size() == 1) {
+            return nums.front();
+        }
+        int twoPreviousMaximumRobbedMoney = nums[0];
+        int previousMaximumRobbedMoney = max(nums[0], nums[1]);
+        for (int i = 2; i < nums.size(); ++i) {
+            int currentMaximumRobbedMoney = max(previousMaximumRobbedMoney, twoPreviousMaximumRobbedMoney + nums[i]);
+            twoPreviousMaximumRobbedMoney = previousMaximumRobbedMoney;
+            previousMaximumRobbedMoney = currentMaximumRobbedMoney;
+        }
+        return previousMaximumRobbedMoney;
+    }
+};

198/step3.cpp

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+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        if (nums.size() == 1) {
+            return nums[0];
+        }
+        vector<int> maximumRobbedMoney(nums.size(), 0);
+        maximumRobbedMoney[0] = nums[0];
+        maximumRobbedMoney[1] = max(nums[0], nums[1]);
+        for (int i = 2; i < nums.size(); ++i) {
+            maximumRobbedMoney[i] = max(maximumRobbedMoney[i - 1], maximumRobbedMoney[i - 2] + nums[i]);
+        }
+        return maximumRobbedMoney.back();
+    }
+};