本日付で、３年ほど勤めたIBMを退職しました。 で、新たに会社を起こすことにしまして、明日から本格稼働します。 Nishika（にしか）という会社です。 www.nishika.com 今日は、起業に至った思いや、やろうとしている事業に至った思いを記録しておきたいと思…

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/ Given an array where elements are sorted in ascending order, convert it to a height balanced BST. For this problem, a height-balanced binary tree is defined as a bin…

https://leetcode.com/problems/binary-tree-level-order-traversal-ii/ Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root). For example: Given binary…

https://leetcode.com/problems/maximum-depth-of-binary-tree/ Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Note: A leaf is a n…

https://leetcode.com/problems/symmetric-tree/ Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmetric: But the following [1,2,2,null,3,null,3…

https://leetcode.com/problems/same-tree/ 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. LeetCode…

https://leetcode.com/problems/merge-sorted-array/ 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 as…

https://leetcode.com/problems/remove-duplicates-from-sorted-list/ Given a sorted linked list, delete all duplicates such that each element appear only once. Example 1: Input: 1->1->2 Output: 1->2 Example 2: Input: 1->1->2->3->3 Output: 1->…

https://leetcode.com/problems/sqrtx/ Implement int sqrt(int x). Compute and return the square root of x, where x is guaranteed to be a non-negative integer. Since the return type is an integer, the decimal digits are truncated and only the…

https://leetcode.com/problems/add-binary/ Given two binary strings, return their sum (also a binary string). The input strings are both non-empty and contains only characters 1 or 0. Example 1: Input: a = "11", b = "1" Output: "100" Exampl…

https://leetcode.com/problems/plus-one/ Given a non-empty array 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…

https://leetcode.com/problems/count-and-say/ The count-and-say sequence is the sequence of integers with the first five terms as following: 1 11 21 1211 111221 1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read of…

https://leetcode.com/problems/length-of-last-word/ Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string. If the last word does not exist, return 0. Note: A wor…

https://leetcode.com/problems/search-insert-position/ Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum. Example: Input: [-2,1,-3,4,-1,2,1,-5,4], Output:…

https://leetcode.com/problems/search-insert-position/ Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order. You may assume no duplicates i…

https://leetcode.com/problems/implement-strstr/ Implement strStr(). Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Example 1: Input: haystack = "hello", needle = "ll" Output: 2 Exam…

https://leetcode.com/problems/remove-element/ Given an array nums and a value val, remove all instances of that value in-place and return the new length. Do not allocate extra space for another array, you must do this by modifying the inpu…

https://leetcode.com/problems/remove-duplicates-from-sorted-array/ Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length. Do not allocate extra space for another array, …

https://leetcode.com/problems/merge-two-sorted-lists/ 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-…

https://leetcode.com/problems/valid-parentheses/ Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same t…

https://leetcode.com/problems/longest-common-prefix/ Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "". Example 1: Input: ["flower","flow","flight…

https://leetcode.com/problems/roman-to-integer/ Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 その名の通り、ローマ数字を数値に変換するという問題です。 "…

https://leetcode.com/problems/palindrome-number/ Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward. Example 1: Input: 121 Output: true Example 2: Input: -121 Output: false E…

この問題はBad評価も多いですが、公式のSolutionと異なる解法が色々Discussionされているという意味で、面白いです。 https://leetcode.com/problems/reverse-integer/ Given a 32-bit signed integer, reverse digits of an integer. Example 1: Input: 123…

19/7/7時点でLeetCodeの第一問目に掲載されている問題ですが、シンプルでいて意外に深みのある良問。 https://leetcode.com/problems/two-sum/ Given an array of integers, return indices of the two numbers such that they add up to a specific target.…

唐突ですが、私のマイブームを紹介します。 leetcode.com LeetCodeという、コーディングの問題集的サイトです。 最近はここで毎日問題を解いているんですが、せっかくなら何かしらアウトプットした方がペースメーカーにもなると思い、ブログ記事にします。 L…