leetcode404

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution
{
    List<TreeNode> list1 = new List<TreeNode>();
        List<TreeNode> list2 = new List<TreeNode>();
        private void postTree(TreeNode root)
        {
            if (root != null)
            {
                if (root.left != null)
                {
                    list1.Add(root.left);
                    postTree(root.left);
                }

                if (root.right != null)
                {
                    postTree(root.right);
                }
                //左叶子，是左子树并且是叶子

                if (root.left == null && root.right == null)//叶子节点
                {
                    //如何判断是左子树呢
                    list2.Add(root);
                }
            }
        }

        public int SumOfLeftLeaves(TreeNode root)
        {
            postTree(root);

            var list = list1.Intersect(list2);

            var sum = 0;

            foreach (var l in list)
            {
                sum += l.val;
            }

            return sum;
        }        
}

https://leetcode.com/problems/sum-of-left-leaves/#/description

补充一个python的实现：

class Solution:
    def __init__(self):
        self.leftsum = 0
    def preOrder(self,root):
        if root != None:
            if root.left != None and root.left.left == None and root.left.right == None:
                self.leftsum += root.left.val
            self.preOrder(root.left)
            self.preOrder(root.right)
            
    def sumOfLeftLeaves(self, root: TreeNode) -> int:
        self.preOrder(root)
        return self.leftsum