diff --git a/0122-best-time-to-buy-and-sell-stock-II/memo.md b/0122-best-time-to-buy-and-sell-stock-II/memo.md
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+### step1
+
+わからなかったのでChatGPTに解いてもらった。株を持っている状態と持っていない状態の最大値を更新していくDP。
+
+### step2
+
+greedyでも解けるということでChatGPTに解いてもらった。最初考えていたが実装できなかったアイデアに近かった。
+https://github.com/naoto-iwase/leetcode/pull/43/changes こちらのコードの実装1も読んでみたが、step2のコードとやってることはほぼ同じだった。
+
+### step3
+
+step1を3回通すまで書き直し。
diff --git a/0122-best-time-to-buy-and-sell-stock-II/step1.cpp b/0122-best-time-to-buy-and-sell-stock-II/step1.cpp
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+++ b/0122-best-time-to-buy-and-sell-stock-II/step1.cpp
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+class Solution {
+public:
+    int maxProfit(vector<int>& prices) {
+        int hold = -prices[0];
+        int not_hold = 0;
+
+        for (int i = 1; i < prices.size(); i++) {
+            int new_hold = max(hold, not_hold - prices[i]);
+            int new_not_hold = max(not_hold, hold + prices[i]);
+
+            hold = new_hold;
+            not_hold = new_not_hold;
+        }
+
+        return not_hold;
+    }
+};
diff --git a/0122-best-time-to-buy-and-sell-stock-II/step2.cpp b/0122-best-time-to-buy-and-sell-stock-II/step2.cpp
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+++ b/0122-best-time-to-buy-and-sell-stock-II/step2.cpp
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+class Solution {
+public:
+    int maxProfit(vector<int>& prices) {
+        int profit = 0;
+        for (int i = 1; i < prices.size(); i++) {
+            if (prices[i] > prices[i - 1]) {
+                profit += prices[i] - prices[i - 1];
+            }
+        }
+        return profit;
+    }
+};
diff --git a/0122-best-time-to-buy-and-sell-stock-II/step3.cpp b/0122-best-time-to-buy-and-sell-stock-II/step3.cpp
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+++ b/0122-best-time-to-buy-and-sell-stock-II/step3.cpp
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+class Solution {
+public:
+    int maxProfit(vector<int>& prices) {
+        int hold = -prices[0];
+        int not_hold = 0;
+
+        for (int i = 1; i < prices.size(); i++) {
+            int new_hold = max(hold, not_hold - prices[i]);
+            int new_not_hold = max(not_hold, hold + prices[i]);
+
+            hold = new_hold;
+            not_hold = new_not_hold;
+        }
+
+        return not_hold;
+    }
+};