Add O(N) code without cache

Author: colorbox

110/step5.cpp

@@ -0,0 +1,30 @@
+// キャッシュを使わずにO(N)となるコード
+class Solution {
+public:
+    bool isBalanced(TreeNode* root) {
+        return getHeight(root) != -1;
+    }
+
+    int getHeight(TreeNode* root) {
+        if (!root) {
+            return 0;
+        }
+
+        int left_height = getHeight(root->left);
+        if (left_height == -1) {
+            return -1;
+        }
+
+        int right_height = getHeight(root->right);
+        if (right_height == -1) {
+            return -1;
+        }
+
+        if (abs(left_height - right_height) > 1) {
+            return -1;
+        }
+
+        return max(left_height, right_height) + 1;
+    }
+
+};