【面試題46】把數字翻譯成字符串

Python題解

class Solution:
    def GetTranslationCount(self, number):
        def helper(number):
            length = len(number)
            counts = [0] * length
            count = 0
            for i in range(length-1, -1, -1):
                count = 0
                if i < length - 1:
                    count = counts[i+1]
                else:
                    count = 1
                if i < length - 1:
                    digit1 = int(number[i]) - int('0')
                    digit2 = int(number[i+1]) - int('0')
                    converted = digit1 * 10 + digit2
                    if converted >= 10 and converted <= 25:
                        if i < length - 2:
                            count += counts[i+2]
                        else:
                            count += 1
                counts[i] = count
            count = counts[0]
            return count
        numberInString = str(number)
        return helper(numberInString)

考點

• 考查分析問題的能力。能夠分析出遞歸的表達式是解決這個問題的前提；
• 考查對遞歸及時間效率的理解。如果只是能夠把遞歸分析轉換爲遞歸代碼，不一定能夠通過這道題的面試，而是能夠用基於循環的代碼來避免不必要的重複計算。