[leetcode]563. Binary Tree Tilt

最新推荐文章于 2018-10-29 23:33:00 发布

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本文介绍了一种计算二叉树每个节点左右子树之差的绝对值，并将所有节点的这种差值相加得到整棵树的倾斜值的方法。通过递归遍历的方式实现，适用于32位整数范围内的节点值。

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Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes' tilt.

Example:

Input: 
         1
       /   \
      2     3
Output: 1
Explanation: 
Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

Note:

The sum of node values in any subtree won't exceed the range of 32-bit integer.

All the tilt values won't exceed the range of 32-bit integer.

分析：题目为求每个节点的左右子树的差的绝对值,再对这些绝对值求和.利用递归搜索.

/**
 * @author binkang
 * @date May 5, 2017
 */
public class BinaryTreeTilt {

	// Definition for a binary tree node.
	class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}

	private int sum = 0;

	public int findTilt(TreeNode root) {
		helper(root);
		return sum;
	}

	private int helper(TreeNode root) {
		if (root == null)
			return 0;
		int left = helper(root.left);
		int right = helper(root.right);
		sum += Math.abs(left - right);
		return root.val + left + right;
	}
}