https://leetcode.com/problems/count-and-say/description/ My GitHub: Count And Say The nth level result is from counting each digit of the result of (n-1) th level.

# Category: Coding Interview

## String to Integer (atoi)

https://leetcode.com/problems/string-to-integer-atoi/description/ github: String to Integer(atoi) Checking point: null or empty string white spaces +/- sign calculate real value handle min & max github: String to Integer(atoi) ** trim white space before checking string is empty, so we can ignore whitespaces before number **

## Using StringBuffer solve Reverse Integer problem

LeetCode: https://leetcode.com/problems/reverse-integer/description/ The below Solution 1 is the most popular solution we can find online. But here is another way (Solution 2) to solve the problem with StringBuffer. The Solution 2 is easier to understand and the code is cleaner. Solution 1: Solution 2:

## leetcode- Rotate Image

Leetcode: https://leetcode.com/problems/rotate-image/description/ Given input matrix = [1,2,3], [4,5,6], [7,8,9] rotate the input matrix in-place such that it becomes: [7,4,1], [8,5,2], [9,6,3] (x, y), the affected point is (y, n – x – 1), (n – x – 1, n – y – 1), (n – y – 1, x), “n” is the size of the matrix. … Continue reading leetcode- Rotate Image

## LeetCode – Plus One

Given a non-negative integer represented as a non-empty array of digits, plus one to the integer. You may assume the integer do not contain any leading zero, except the number 0 itself. The digits are stored such that the most significant digit is at the head of the list. For example: Q1. int[] nums = {1,2,3,4}; int[] … Continue reading LeetCode – Plus One

## How to check if a string has all unique characters

GitHub: solution 1.1 Check if the string is an ASCII string. There are many different solutions, I practiced with a HashSet. Time complexity: O (n). from Cracking the Code Interview , isUniqueChars2 is an insteresting solution. A good source to explain the solution: trying to understand: checker |= (1 << val) Reference: http://javahungry.blogspot.com/2014/11/string-has-all-unique-characters-java-example.html https://www.codeproject.com/Articles/760162/How-to-check-if-a-string-has-all-unique-characters

## LeetCode – Two Sum II

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number. CheckPoint: if (numbers != null && numbers.length > 1) {throw new IllegalArgumentException("No solution!");} 1st: 2nd:

## Array Implementation of Queue (Fixed size)

github:arrayQueue.java. Purpose: reuse a fixed size array. ----> Tracking 2 variables frontIndex for deletion and rearIndex for insertion. CheckPoint: array size > 0. isEmpty() Check rearIndex == frontIndex. Enqueue --> queue is full. Dequeue --> queue is empty. Complexity Analysis: Time complexity : enqueue: O(1) assign the value to array[rearIndex] dequeue: O(1) move frontIndex to next … Continue reading Array Implementation of Queue (Fixed size)

## Implement Queue using Stacks

github: ImplementQueueusingStacks.java Using 2 stacks- s1 and s2 to implement a queue. Purpose: keep the input on the bottom of s1 The idea is that when an input comes, we push the input to s1, BUT only if the s1 is empty. If s1 is not empty then we pop out all element from s1 and … Continue reading Implement Queue using Stacks

## Palindrome Checker

github: Palindrome.java A few good ways to remove space from a string. Method 1 private static String removeSpace(String aword) { StringBuilder buffer = new StringBuilder(); for (int i = 0; i < aword.length(); i++) { if (aword.charAt(i) != ' ')) { buffer.append(aword.charAt(i)); } } return buffer.toString(); } Method 2 //Removing all white spaces … Continue reading Palindrome Checker