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Leetcode Problem 437. Path Sum III

437. Path Sum III

Leetcode Solutions

Prefix Sum Approach for Path Sum III

  1. Initialize a counter count to 0 to store the number of valid paths.
  2. Initialize a hashmap h to store the frequency of prefix sums.
  3. Define a recursive function preorder(node, curr_sum) that takes the current node and the current prefix sum as arguments.
  4. Inside preorder, add the value of the current node to curr_sum.
  5. If curr_sum equals the target sum, increment count by 1.
  6. Increment count by the frequency of curr_sum - targetSum from the hashmap.
  7. Increment the frequency of curr_sum in the hashmap by 1.
  8. Recursively call preorder for the left and right children of the current node with the updated curr_sum.
  9. After the recursive calls, decrement the frequency of curr_sum in the hashmap by 1 to avoid counting paths from parallel subtrees.
  10. Return the value of count after the traversal is complete.
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DFS with Path Tracking Approach for Path Sum III

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