摘要： Path sum: two waysIn the 5 by 5 matrix below, the minimal path sum from the top left to the bottom right, byonly moving to the right and down, is indi... 阅读全文

摘要： Square root digital expansionIt is well known that if the square root of a natural number is not an integer, then it is irrational. The decimal expans... 阅读全文

摘要： Passcode derivationA common security method used for online banking is to ask the user for three random characters from a passcode. For example, if th... 阅读全文