2021-10-17 Daily-Challenge

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Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 17

Description

Path Sum III

Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum.

The path does not need to start or end at the root or a leaf, but it must go downwards (i.e., traveling only from parent nodes to child nodes).

Example 1:

img

Input: root = [10,5,-3,3,2,null,11,3,-2,null,1], targetSum = 8
Output: 3
Explanation: The paths that sum to 8 are shown.

Example 2:

Input: root = [5,4,8,11,null,13,4,7,2,null,null,5,1], targetSum = 22
Output: 3

Constraints:

  • The number of nodes in the tree is in the range [0, 1000].
  • -10^9 <= Node.val <= 10^9
  • -1000 <= targetSum <= 1000

Solution

class Solution {
  int sum;
  int ans;
  void dfs(TreeNode* root, int cur, bool inPath) {
    if(!root) return;
    if(cur == root->val) ans += 1;
    if(!inPath) {
      dfs(root->left, cur, false);
      dfs(root->right, cur, false);
    }
    dfs(root->left, cur-root->val, true);
    dfs(root->right, cur-root->val, true);
  }
public:
  int pathSum(TreeNode* root, int sum) {
    if(!root) return 0;
    this->sum = sum;
    dfs(root, sum, false);
    return ans;
  }
};

// Accepted
// 126/126 cases passed (20 ms)
// Your runtime beats 66.65 % of cpp submissions
// Your memory usage beats 77.5 % of cpp submissions (15.7 MB)
Algorithm