LeetCode: Balanced Binary Tree 解題報告

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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.

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SOLUTION 1:

使用inner Class來解決

 1 // Solution 1: 2     public boolean isBalanced1(TreeNode root) { 3         return dfs(root).isBalanced; 4     } 5      6     // bug 1: inner class is like:  "public class ReturnType {", no () 7     public class ReturnType { 8         boolean isBalanced; 9         int depth;10         11         ReturnType(int depth, boolean isBalanced) {12             this.depth = depth;13             this.isBalanced = isBalanced;14         }15     }16     17     public ReturnType dfs(TreeNode root) {18         ReturnType ret = new ReturnType(0, true);19         20         if (root == null) {21             return ret;22         }23         24         ReturnType left = dfs(root.left);25         ReturnType right = dfs(root.right);26         27         ret.isBalanced = left.isBalanced 28                          && right.isBalanced 29                          && Math.abs(left.depth - right.depth) <= 1;30                          31         // bug 2: remember to add 1( the root depth )                 32         ret.depth = Math.max(left.depth, right.depth) + 1;33         34         return ret;35     }

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SOLUTION 2:

將 get depth函數提出

 1 // Solution 2: 2     public boolean isBalanced(TreeNode root) { 3         if (root == null) { 4             return true; 5         }         6          7         return isBalanced(root.left) && isBalanced(root.right) 8             && Math.abs(getDepth(root.left) - getDepth(root.right)) <= 1; 9     }10     11     public int getDepth(TreeNode root) {12         if (root == null) {13             return 0;14         }15         16         return Math.max(getDepth(root.left), getDepth(root.right)) + 1;17     }

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GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/tree/IsBalanced.java

LeetCode: Balanced Binary Tree 解題報告