112. Path Sum

import java.util.Stack;

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

    public class Flag{
        public boolean res;
    }
    
    public boolean hasPathSum(TreeNode root, int sum) {
        // 主要思想是深度优先遍历
        if(root==null)
            return false;
        Flag flag=new Flag();
        flag.res=false;
        DFS(root,sum,0,flag);
        
        return flag.res;
        
        
    }
    
    public static void DFS(TreeNode root,int sum,int total,Flag flag)
    {
        if(root.left==null&&root.right==null)
        {
            if(sum==total+root.val)
                flag.res=true;
            return ;
        }
        if(root.left!=null)
        {
            DFS(root.left,sum,total+root.val,flag);
        }
        
        if(root.right!=null)
        {
            DFS(root.right,sum,total+root.val,flag);
        }
    }
}