Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

Given two arrays of length m and n with digits 0-9 representing two numbers. Create the maximum number of length k <= m + n from digits of the two. The relative...

You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your frie...

Given a string that contains only digits 0-9 and a target value, return all possibilities to add binary operators (not unary) +, -, or * between the digits so t...

Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.

CIA has decided to create a special telephone directory for its agents. The first 2 pages of the directory contain the name of the directory and instructions fo...

Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2.

Given a 32-bit signed integer, reverse digits of an integer.

**解析：**Version 1，先将数字n变为字符数组，要找最小的大于n的数，则应该从右往左开始，依次寻找第i位字符右边的大于当前字符的最小数字，然后互换二者位置，由于新数字的第i位字符大于n中的第i位字符，因此新数字i位之后的字符应...