Sponsored
Sponsored
This approach involves using recursive DFS to traverse the tree. At each node, determine if it is a left leaf. If it is, add its value to the sum and recursively continue to search for more left leaves in the subtree.
The time complexity is O(n) where n is the number of nodes, as we visit each node once. The space complexity is O(h), where h is the height of the tree, due to the recursive call stack.
1#include <stdio.h>
2#include <stdlib.h>
3
4struct TreeNode {
5 int val;
6 struct TreeNode *left;
7 struct TreeNode *right;
8};
9
10int dfs(struct TreeNode* node, int isLeft) {
11 if (node == NULL) return 0;
12 if (node->left == NULL && node->right == NULL && isLeft) return node->val;
13 return dfs(node->left, 1) + dfs(node->right, 0);
14}
15
16int sumOfLeftLeaves(struct TreeNode* root) {
17 return dfs(root, 0);
18}We define a helper function dfs which takes a node and a boolean indicating whether it is a left child. If the node is a leaf and is a left child, we add its value to the sum. Otherwise, recurse into the left and right subtrees.
This approach applies iterative DFS using a stack. By exploring each node iteratively, it checks if a node qualifies as a left leaf and accumulates its value to the sum. It manages to mimic a recursive pattern iteratively.
The time complexity is O(n) for navigating each tree node once. Space complexity is O(n) due to maintaining a stack proportional to the number of nodes.
1using System;
using System.Collections.Generic;
public class TreeNode {
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int x) { val = x; }
}
public class Solution {
public int SumOfLeftLeaves(TreeNode root) {
if (root == null) return 0;
int sum = 0;
Stack<(TreeNode node, bool isLeft)> stack = new Stack<(TreeNode, bool)>();
stack.Push((root, false));
while (stack.Count > 0) {
var (node, isLeft) = stack.Pop();
if (node.left == null && node.right == null && isLeft) {
sum += node.val;
}
if (node.right != null) {
stack.Push((node.right, false));
}
if (node.left != null) {
stack.Push((node.left, true));
}
}
return sum;
}
}C# utilizes tuple usage within stack operations to manage the node traversal iteratively. Efforts revolve around ensuring all node visitation and left leaf value accumulation are vigilantly observed.