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.
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 **
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: