Add cache code

Author: colorbox

110/step4.cpp

@@ -0,0 +1,30 @@
+// 繰り返し呼ばれるheightについて、キャッシュで高速化を試みたがむしろ低速化した
+class Solution {
+public:
+    bool isBalanced(TreeNode* root) {
+        if (!root) {
+            return true;
+        }
+
+        int left_height = height(root->left);
+        int right_height = height(root->right);
+
+        return abs(right_height - left_height) <= 1 && isBalanced(root->left) && isBalanced(root->right);
+    }
+
+    map<TreeNode*, int> height_cache;
+    int height(TreeNode* root, int base_height = 0) {
+        if (height_cache.count(root)) {
+            return height_cache[root];
+        }
+        if (!root) {
+            return base_height;
+        }
+
+        int left_height = height(root->left);
+        int right_height = height(root->right);
+
+        height_cache[root] = max(left_height, right_height)+1;
+        return height_cache[root];
+    }
+};