README_EN.md

129. Sum Root to Leaf Numbers

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Description

You are given the root of a binary tree containing digits from 0 to 9 only.

Each root-to-leaf path in the tree represents a number.

• For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.

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

A leaf node is a node with no children.

 

Example 1:

Input: root = [1,2,3]
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: root = [4,9,0,5,1]
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

 

Constraints:

• The number of nodes in the tree is in the range [1, 1000].
• 0 <= Node.val <= 9
• The depth of the tree will not exceed 10.

Solutions

DFS.

Python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def sumNumbers(self, root: TreeNode) -> int:
        def dfs(root, presum):
            if root is None:
                return 0
            s = 10 * presum + root.val
            if root.left is None and root.right is None:
                return s
            return dfs(root.left, s) + dfs(root.right, s)

        return dfs(root, 0)

Java

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

    private int dfs(TreeNode root, int presum) {
        if (root == null) {
            return 0;
        }
        int s = presum * 10 + root.val;
        if (root.left == null && root.right == null) {
            return s;
        }
        return dfs(root.left, s) + dfs(root.right, s);
    }
}

TypeScript

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

function sumNumbers(root: TreeNode | null): number {
    return dfs(root);
};

function dfs(root: TreeNode | null, preSum : number = 0): number {
    if (!root) return 0;
    preSum = preSum * 10 + root.val;
    if (!root.left && !root.right) return preSum;
    return dfs(root.left, preSum) + dfs(root.right, preSum);
}

C++

/**
 * 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:
    int sumNumbers(TreeNode *root) {
        return dfs(root, 0);
    }

    int dfs(TreeNode *root, int presum) {
        if (root == nullptr)
            return 0;
        int s = presum * 10 + root->val;
        if (root->left == nullptr && root->right == nullptr)
            return s;
        return dfs(root->left, s) + dfs(root->right, s);
    }
};

Go

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumNumbers(root *TreeNode) int {
	return dfs(root, 0)
}

func dfs(root *TreeNode, presum int) int {
	if root == nil {
		return 0
	}
	s := presum*10 + root.Val
	if root.Left == nil && root.Right == nil {
		return s
	}
	return dfs(root.Left, s) + dfs(root.Right, s)
}

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