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+## 何も見ずに解いてみる
+
+```cpp
+class Solution {
+public:
+    double myPow(double x, long long n) {
+        if (n == 0) {
+            return 1;
+        }
+        if (n < 0) {
+            return 1 / myPow(x, -n);
+        }
+        vector<long long> power_of_2_cache = {1};
+        while (power_of_2_cache.size() < 32) {
+            long long new_power_of_2 = power_of_2_cache.back() * 2;
+            if (new_power_of_2 > n) {
+                break;
+            }
+            power_of_2_cache.push_back(new_power_of_2);
+        }
+        vector<int> n_components_in_power_of_2;
+        for (int exp = power_of_2_cache.size() - 1; exp >= 0; --exp) {
+            if (power_of_2_cache[exp] <= n) {
+                n -= power_of_2_cache[exp];
+                n_components_in_power_of_2.push_back(exp);
+            }
+        }
+        vector<double> power_of_x_cache = {x};
+        for (int exp = 1; exp <= n_components_in_power_of_2.front(); ++exp) {
+            power_of_x_cache.push_back(power_of_x_cache.back() * power_of_x_cache.back());
+        }
+        double result = 1;
+        for (int component : n_components_in_power_of_2) {
+            result *= power_of_x_cache[component];
+        }
+        return result;
+    }
+};
+```
+
+n == -2^31 の時に-nがintにcastできなくてエラーになった（intの表現範囲が-2^31 <= n <= 2^31 - 1のため）のでとりあえず関連する型を全部long longにして無理やり通しました  
+
+## 他の人のコードを見てみる
+
+https://github.com/tokuhirat/LeetCode/pull/45/files  
+https://github.com/ryosuketc/leetcode_arai60/pull/34/files  
+https://github.com/Ryotaro25/leetcode_first60/pull/48  
+
+自分は非常に面倒なことをしていたらしい。。。
+
+## 最終コード
+
+```cpp
+class Solution {
+public:
+    double myPow(double x, int n) {
+        if (n == 0) {
+            return 1.0;
+        }
+        if (n < 0) {
+            // cast to long long to handle INT_MIN;
+            return 1.0 / _myPow(x, -(long long)n);
+        }
+        return _myPow(x, n);
+    }
+private:
+    double _myPow(double x, long long n) {
+        double result = 1.0;
+        while (n) {
+            if (n % 2 == 1) {
+                result *= x;
+            }
+            x *= x;
+            n /= 2;
+        }
+        return result;
+    }
+};
+```