Today I have done Path Sum on leetcode and leetcode's December LeetCoding Challenge with cpp.

Path Sum

Description

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

nothing to say

class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) {
        if(!root) return false;
        if(root->left || root->right) return hasPathSum(root->left, sum-root->val) || hasPathSum(root->right, sum-root->val);
        return sum == root->val;
    }
};

December LeetCoding Challenge 24

Description

Swap Nodes in Pairs

Given a linked list, swap every two adjacent nodes and return its head.

You may not modify the values in the list's nodes. Only nodes itself may be changed.

Example 1:

Input: head = [1,2,3,4]
Output: [2,1,4,3]

Example 2:

Input: head = []
Output: []

Example 3:

Input: head = [1]
Output: [1]

Constraints:

• The number of nodes in the list is in the range [0, 100].
• 0 <= Node.val <= 100

Solution

nothing to say

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        ListNode *newHead = new ListNode(-1, head);
        ListNode *cur = newHead;
        while(cur->next && cur->next->next) {
            ListNode *nxt = cur->next;
            cur->next = nxt->next;
            nxt->next = cur->next->next;
            cur->next->next = nxt;
            cur = cur->next->next;
        }
        return newHead->next;
    }
};