You have 4 cards each containing a number from 1 to 9. You need to judge whether they could operated through *, /, +, -, (, )to get the value of 24.

Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell.

There is a fence with n posts, each post can be painted with one of the k colors.

A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).