Leetcode 404(Java)

Find the sum of all left leaves in a given binary tree.

Example:

3

/ \
9 20
/ \
15 7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

sum为所有左枝叶子结点的和，采用DFS递归调用SumOfLeftLeaves()，判断当前结点左子结点非空后，在判断其是否叶子结点，若是则将其值加入sum中，AC码如下：

public class Solution {
    int sum=0;
    public int sumOfLeftLeaves(TreeNode root) {
        if(root==null)return 0;
        if(root.left!=null){
            if(root.left.left==null && root.left.right==null){
                sum+=root.left.val;
            }else{
                sumOfLeftLeaves(root.left);
            }
        }
        sumOfLeftLeaves(root.right);
        return sum;
    }
}