Path Sum

1.题目

判断是否从根到叶子的路径和跟给定sum相同的

Given the below binary tree and sum = 22,

              5             / \            4   8           /   / \          11  13  4         /  \      \        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

2.算法

用递归法，看看左子树或右子树有没有满足条件的路径

    public boolean hasPathSum(TreeNode root, int sum) {          if(root == null)              return false;          if(root.left == null && root.right==null && root.val==sum)              return true;          return hasPathSum(root.left, sum-root.val) || hasPathSum(root.right, sum-root.val);      }