Balanced Binary Tree

Author: int32bit

README.md

@@ -30,6 +30,7 @@
 + [100 Same Tree](algorithms/SameTree)
 + [101 Symmetric Tree](algorithms/SymmetricTree)
 + [104 Maximum Depth of Binary Tree](algorithms/MaximumDepthofBinaryTree)
++ [110 Balanced Binary Tree](algorithms/BalancedBinaryTree)
 + [111 Minimum Depth of Binary Tree](algorithms/MinimumDepthofBinaryTree)
 + [112 Path Sum(前序遍历)](algorithms/PathSum)
 + [113 Path Sum II(前序遍历)](algorithms/PathSum2)

algorithms/BalancedBinaryTree/'

@@ -0,0 +1,29 @@
+#include <cstdlib>
+using namespace std;
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+class Solution {
+public:
+    bool isBalanced(TreeNode *root) {
+	    if (root == NULL)
+		    return true;
+	    if (root->left && root->right)
+		    return isBalanced(root->left) && isBalanced(root->right);
+	    if (root->left) {
+		    return root->left->left && !root->left->right;
+		    if (root->left->left || root->left->right)
+			    return false;
+		    else
+			    return true;
+	    }
+    }
+
+};
+int main(int argc, char **argv)
+{
+	return 0;
+}

algorithms/BalancedBinaryTree/README.md

@@ -0,0 +1,30 @@
+## Balanced Binary Tree
+
+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 depth of the two subtrees of every node never differ by more than 1. 
+
+## Solution
+
+分别求左右子树的高度，如果高度之差大于1，则不是平衡树
+
+而如果子树不是平衡树，结果也一定不是平衡树，因此再求左右子树的同时，顺便判断是否平衡树，能够提高速度
+
+## Code
+```cpp
+bool isBalanced(TreeNode *root) {
+	    bool unbalenced = false;
+	    getHeight(unbalenced, root);
+	    return !unbalenced;
+}
+int getHeight(bool &unbalenced, TreeNode *root) {
+    if (root == NULL || unbalenced)
+	    return -1;
+    int left = getHeight(unbalenced, root->left);
+    int right = getHeight(unbalenced, root->right);
+    if (abs(left, right) > 1) {
+	    unbalenced = true;
+    }
+    return 1 + (left > right ? left : right);
+}
+```

algorithms/BalancedBinaryTree/solve.cpp

@@ -0,0 +1,35 @@
+#include <cstdlib>
+using namespace std;
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+static inline int abs(int a, int b)
+{
+	return a > b ? a - b : b - a;
+}
+class Solution {
+public:
+    bool isBalanced(TreeNode *root) {
+	    bool unbalenced = false;
+	    getHeight(unbalenced, root);
+	    return !unbalenced;
+    }
+    int getHeight(bool &unbalenced, TreeNode *root) {
+	    if (root == NULL || unbalenced)
+		    return -1;
+	    int left = getHeight(unbalenced, root->left);
+	    int right = getHeight(unbalenced, root->right);
+	    if (abs(left, right) > 1) {
+		    unbalenced = true;
+	    }
+	    return 1 + (left > right ? left : right);
+    }
+
+};
+int main(int argc, char **argv)
+{
+	return 0;
+}