Sum Root to Leaf Numbers

iteye_6755

于 2015-09-11 14:00:12 发布

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本文介绍了一种算法，用于求解二叉树中所有从根节点到叶子节点的路径所表示数字的总和。通过递归方法遍历每个可能的路径，并计算其数值，最终得到所有路径数值之和。

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Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
    	return solve(root, 0);
    }

	private int solve(TreeNode root, int level) {
		if (root == null) {
        	return 0;
        }
        if (root.left==null && root.right==null) {
        	return  level + root.val;
        }
        int nextLevel = (level + root.val) * 10;
        int left = solve(root.left, nextLevel);
        int right = solve(root.right, nextLevel);
        return left + right;
	}
}