404. Sum of Left Leaves

Problem Statement

Given the root of a binary tree, return the sum of all left leaves.

A leaf is a node with no children. A left leaf is a leaf that is the left child of another node.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 24
Explanation: There are two left leaves in the binary tree, with values 9 and 15 respectively.

Example 2:

Input: root = [1]
Output: 0

Constraints:

The number of nodes in the tree is in the range [1, 1000].
-1000 <= Node.val <= 1000

Solution:

package main

// Definition for a binary tree node.
type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

// Recursion
func sumOfLeftLeaves(root *TreeNode) int {
	if root == nil {
		return 0
	}

	// if root.Left is a leaf node
	if root.Left != nil && root.Left.Left == nil && root.Left.Right == nil {
		return root.Left.Val + sumOfLeftLeaves(root.Right)
	}

	return sumOfLeftLeaves(root.Left) + sumOfLeftLeaves(root.Right)
}

// Iteration
func sumOfLeftLeaves2(root *TreeNode) int {
	if root == nil {
		return 0
	}

	sum := 0
	stack := []*TreeNode{root}

	for len(stack) > 0 {
		// pop
		node := stack[len(stack)-1]
		stack = stack[:len(stack)-1]

		if node.Left != nil {
			// if node.Left is a leaf node
			if node.Left.Left == nil && node.Left.Right == nil {
				sum += node.Left.Val
			} else {
				stack = append(stack, node.Left)
			}
		}

		if node.Right != nil {
			stack = append(stack, node.Right)
		}
	}

	return sum
}

404. Sum of Left Leaves #

Problem Statement #

Solution: #

... #

404. Sum of Left Leaves

Problem Statement

Solution:

...