题解 | 二叉树中和为某一值的路径(一)

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

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 bool布尔型
     */
    public boolean hasPathSum (TreeNode root, int sum) {
        // write code here

        if (root == null) return false;

        Stack<TreeNode> stack = new Stack<TreeNode>();

        TreeNode node = root;
        TreeNode pre = null;
        int totalNumber = 0;
        while (!stack.isEmpty() || node != null) {

            while (node != null) {
                totalNumber += node.val;
                stack.push(node);
                node = node.left;
                
            }

            if (!stack.isEmpty()) {

                node = stack.pop();
                totalNumber = totalNumber - node.val;
                if (node.right == null || node.right == pre) {

                    if (node.left == null && node.right == null && totalNumber + node.val == sum) {
                        return true;
                    }
                    pre = node;
                    node = null;
                } else {
                    totalNumber += node.val;
                    stack.push(node);
                    node = node.right;
                }
            }

        }

        return false;
    }
}