Leetcode 246

This solution is pretty simple and pretty similar to Leetcode 163.

The problem asks us to flip a number by 180 degrees and then return true if the fliped number is equal to the non-fliped number.

You might think that just flipping every digit and then check whether the following fliped number is equal to the non fliped number, but there is a problem with just flipping. Here is an example to show that just flipping doesn’t work:

input: "69" expected output: true.

If we flip every digit, we get 6 converts to 9 and 9 flips to 6, so we get 96. When we compare 96 == 69, we have to return false even though we want it to output true.

But if we reverse the fliped string and then compare it with the original string, we get the proper output. This can be shown with some images:

The Code:

func isStrobogrammatic(num string) bool {
    newNumber := ""
    for i := len(num) - 1; i >= 0; i-- {
        lastDigit := num[i]
        switch lastDigit {
        case '0':
            newNumber += "0"
        case '1':
            newNumber += "1"
        case '6':
            newNumber += "9"
        case '8':
            newNumber += "8"
        case '9':
            newNumber += "6"
        default:
            return false
        }
    }
    return newNumber == num
}