알고리즘 트레이닝/LeetCode

문제 Given the root of a binary tree, return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3,9,20,null,null,15,7] Output: 3Example 2: Input: root = [1,null,2] Output: 2Example 3: Input: root = [] Output: 0Example 4: Input: root = [0] Output: 1Constraints: The number of ..

문제 Given anon-emptyarray of digits representing a non-negative integer, plus one to the integer. The digits are stored such that the most significant digit is at the head of the list, and each element in the array contain a single digit. You may assume the integer does not contain any leading zero, except the number 0 itself. Example 1: Input: [1,2,3] Output: [1,2,4] Explanation: The array repre..

문제 You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself. Example: Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8 Explanation: 342 ..

문제 Given two binary trees, write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical and the nodes have the same value. Example 1: Input: 1 1 / \ / \ 2 3 2 3 [1,2,3], [1,2,3] Output: trueExample 2: Input: 1 1 / \ 2 2 [1,2], [1,null,2] Output: falseExample 3: Input: 1 1 / \ / \ 2 1 1 2 [1,2,1], [1,1,2] Output: false풀이 class ..

문제 Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array. Note: The number of elements initialized in nums1 and nums2 are m and n respectively. You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. Example: Input: nums1 = [1,2,3,0,0,0], m = 3 nums2 = [2,5,6], n = 3 Output: [1,2,2,3,5,6]풀이 ..

문제 Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. Example: Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4 풀이 Divide & Conquer 전략에 따라 작은 문제를 해결하고, 이를 조합하여 큰 문제를 해결한다. class Solution: def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode: if l1 is None : return l2 if l2 is None : return l1 if..

문제 Given a sorted linked list, delete all duplicates such that each element appear only once. Example 1: Input: 1->1->2 Output: 1->2Example 2: Input: 1->1->2->3->3 Output: 1->2->3풀이 정렬된 단일연결리스트를 순회하며 중복(동일값) 여부를 확인하여 제거한다. class Solution: def deleteDuplicates(self, head: ListNode) -> ListNode: cur = head while cur : if cur.next and cur.val == cur.next.val : cur.next = cur.next.next else : cur = ..

문제 You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Note: Given n will be a positive integer. Example 1: Input: 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 stepsExample 2: Input: 3 Output: 3 Explanation: There are three ways to climb to..