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by Sumit Chourasia | Oct 06, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Path Sum - Tree - Easy - LeetCode

Path Sum - Tree - Easy - LeetCode

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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public bool HasPathSum(TreeNode root, int sum) {
        if(root == null){
            return false;
        }
        
        if(root.left == null && root.right == null){
            return root.val==sum;
        }
         
        return HasPathSum(root.left, sum-root.val)||HasPathSum(root.right,sum-root.val);
    }
}

Time Complexity: O(n)

Space Complexity: O(1)

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