Leetcode brush question: binary tree 14 (sum of left leaves)

404. Sum of left leaves

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Calculate the sum of all the left leaves of a given binary tree .

Example ：

Recursive traversal , If it is Left node And it is a leaf node , Just add up the values .

package com.programmercarl.tree;

import com.programmercarl.util.GenerateTreeNode;

/** * @ClassName SumOfLeftLeaves * @Descriotion TODO * @Author nitaotao * @Date 2022/7/5 10:54 * @Version 1.0 * https://leetcode.cn/problems/sum-of-left-leaves/ * 404.  Sum of left leaves  **/
public class SumOfLeftLeaves {
    
    Integer sum = 0;

    public int sumOfLeftLeaves(TreeNode root) {
    
        traversal(root, false);
        return sum;
    }

    public boolean traversal(TreeNode root, boolean isLeft) {
    
        if (root == null) {
    
            // Is it a leaf node 
            return true;
        }
        boolean leftLeaf = traversal(root.left, true);
        // Is it a left leaf node 
        if (leftLeaf && isLeft && root.left == null && root.right == null) {
    
            sum += root.val;
        }
        traversal(root.right, false);
        return false;
    }

    public static void main(String[] args) {
    
        TreeNode root = GenerateTreeNode.generateTreeNode("[0,2,4,1,null,3,-1,5,1,null,6,null,8]");
        System.out.println(new SumOfLeftLeaves().sumOfLeftLeaves(root));

    }
}