Create 110. Balanced Binary Tree.cpp

Author: NeoYY

Diff for: 110. Balanced Binary Tree.cpp

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+/*
+Given a binary tree, determine if it is height-balanced.
+
+For this problem, a height-balanced binary tree is defined as:
+
+a binary tree in which the left and right subtrees of every node differ in height by no more than 1.
+
+ 
+
+Example 1:
+
+Given the following tree [3,9,20,null,null,15,7]:
+
+    3
+   / \
+  9  20
+    /  \
+   15   7
+Return true.
+
+Example 2:
+
+Given the following tree [1,2,2,3,3,null,null,4,4]:
+
+       1
+      / \
+     2   2
+    / \
+   3   3
+  / \
+ 4   4
+Return false.
+*
+
+
+Solution 1 O(n2), Solution O(n)
+
+/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool isBalanced(TreeNode* root) {
+        if ( !root ) return true;
+        if ( !isBalanced( root->left ) ) return false;
+        if ( !isBalanced( root->right ) ) return false;
+        int DepthLeft = Depth( root->left );
+        int DepthRight = Depth( root->right );
+        if ( abs( DepthLeft - DepthRight ) > 1 ) return false;
+        return true;
+    }
+    int Depth( TreeNode *root )
+    {
+        if ( !root ) return 0;
+        return max( Depth( root->left ), Depth( root->right ) ) + 1;
+    }
+};
+
+class Solution {
+public:
+    bool isBalanced(TreeNode* root) {
+        int height = 0;
+        return Balanced( root, height );
+    }
+    bool Balanced( TreeNode *root, int &height )
+    {
+        if ( !root ) return true;
+        int left = 0;
+        int right = 0;
+        if ( !Balanced( root->left, left ) ) return false;
+        if ( !Balanced( root->right, right ) ) return false;
+        if ( abs( left - right ) > 1 ) return false;
+        height = max( left, right ) + 1;
+        return true;
+    }
+};