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Path Sum

Certification: Basic Level Accuracy: 0% Submissions: 0 Points: 5

Given the root of a binary tree and an integer targetSum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum. A leaf is a node with no children.

Example 1
    
  
  • Input: root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
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  • Output: true
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  • Explanation:

     Step 1: Start from the root (5)

     Step 2: Follow the path: 5 -> 4 -> 11 -> 2

     Step 3: Sum the values: 5 + 4 + 11 + 2 = 22
    Step 4: Since the sum equals the target and the path ends at a leaf node, return true
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Example 2
    
  
  • Input: root = [1,2,3], targetSum = 5
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  • Output: false
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  • Explanation:

     Step 1: Start from the root (1)

     Step 2: Follow path 1: 1 -> 2 = 3 (not equal to targetSum)

     Step 3: Follow path 2: 1 -> 3 = 4 (not equal to targetSum)

     Step 4: No root-to-leaf path sums to 5, so return false
    •
Constraints
    
  
  • The number of nodes in the tree is in the range [0, 5000]
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  • -1000 <= Node.val <= 1000
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  • -1000 <= targetSum <= 1000
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  • Time Complexity: O(n) where n is the number of nodes
    • 
  
  • Space Complexity: O(h) where h is the height of the tree
    •
TreeHCL TechnologiesLTIMindtree
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Hint
Solution

Solution Hints

    
  
  • Use a recursive depth-first search approach
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  • At each node, subtract its value from the target sum
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  • If you reach a leaf node and the remaining sum equals the node's value, return true
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  • If you reach a leaf node and the remaining sum doesn't equal the node's value, return false
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  • For non-leaf nodes, recursively check both left and right subtrees
    •

Steps to solve by this approach:

 Step 1: Check if the root is NULL. If so, return false as an empty tree has no paths.

 Step 2: Subtract the current node's value from the target sum.

 Step 3: Check if the current node is a leaf (no left or right children).

 Step 4: If it's a leaf and the remaining target sum is 0, we've found a valid path, so return true.

 Step 5: If it's not a leaf, recursively check both left and right subtrees with the updated target sum.

 Step 6: Return true if either the left or right subtree contains a valid path, otherwise return false.

 Step 7: The recursion will naturally backtrack, effectively "adding back" node values as it returns from deeper levels.

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