leetcode-404. Sum of Left Leaves

404. Sum of Left Leaves

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.

就是简单的遍历二叉树，加一个判定条件是否为左叶子节点就行

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */


class Solution {
    int sum = 0;
    public int sumOfLeftLeaves(TreeNode root) {
        Tra(root,0);
        return sum;
    }
    public  void Tra(TreeNode t,int n){
        if(t==null) return ;
        if(n==1&&t.left==null&&t.right==null) sum+=t.val;
        Tra(t.left,1);
        Tra(t.right,2);
    }
}