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112. Path Sum

2019/12/04 Leetcode

112. Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

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.

Solution

方法1： Recursion DFS

public boolean hasPathSum(TreeNode root, int sum) {
     if (root == null) {
          return false;
     }

     sum -= root.val;
     if (root.left == null && root.right == null) {
          return sum == 0;
     }

     return hasPathSum(root.left, sum) || hasPathSum(root.right, sum);
}

方法2 Iteration Using Stack

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