leetcode-404. Sum of Left Leaves

Posted 2020-09-06 世人谓我恋长安，其实只恋长安某

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.
求所有的左叶子节点的和
java代码:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private void searchBT(TreeNode root, int[] sum){
        if(root.left!=null){
        if(root.left.left==null&&root.left.right==null)sum[0]+=root.left.val;
        }
        if(root.left!=null)searchBT(root.left,sum);
        if(root.right!=null)searchBT(root.right,sum);
    }
    public int sumOfLeftLeaves(TreeNode root) {
        int[] sum={0};////要是调用函数时改变sum的值，只有将其声明为对象，所以这里将其声明为int[]
        if(root!=null)searchBT(root,sum);
        return sum[0];
    }
}