Find the sum of all left leaves in a given binary tree.
左树的值(9+15=24)
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public int sumOfLeftLeaves(TreeNode root) { if(root==null){ return 0; }; int ans=0; Stack<TreeNode> stack=new Stack<TreeNode>(); stack.push(root); while(!stack.empty()){ TreeNode node=stack.pop(); if(node.left!=null&&node.left.left==null&&node.left.right==null){ ans+=node.left.val; } if(node.right!=null){ stack.push(node.right); } if(node.left!=null){ stack.push(node.left); } } return ans; } }