层次遍历+递归

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */
import java.util.*;
public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param sum int整型 
     * @return int整型
     */
    int count;
    public int FindPath (TreeNode root, int sum) {
        // write code here
        if(root==null) return 0;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(queue.size()!=0){
            TreeNode tmp = queue.poll();
            findpath(tmp, sum);
            if(tmp.left!=null) queue.add(tmp.left);
            if(tmp.right!=null) queue.add(tmp.right);
        }
        return count;
    }
    void findpath(TreeNode root, int sum) {
        // write code here
        if(root==null) return;        
        if(sum==root.val) count++;
        findpath(root.left,sum-root.val);
        findpath(root.right,sum-root.val);
    }
}