每日一练7.12——将数字转换为字符串

将数字转换为字符串

# 递归解法
class Solution:
    def translateNum(self, num: int) -> int:
        def trans(num):
            if len(num) <= 1:
                return 1
            
            count = 0
            count += trans(num[1:])
            if num[0] != "0" and int(num[:2]) < 26:
                count += trans(num[2:])
            return count
        return trans(str(num))


# 二分
class Solution:
    def translateNum(self, num: int) -> int:
        num = str(num)
        def trans(begin, end):
            if end - begin <= 0:
                return 1
            mid = begin + (end - begin) // 2
            flag = 0
            p = trans(begin, mid)
            q = trans(mid + 1, end)
            if 1 <= int(num[mid]) <= 2 and int(num[mid:mid + 2]) < 26:
                flag = trans(begin, mid - 1) * trans(mid + 2, end)
            return p * q + flag
        return trans(0, len(num) - 1)

# 动态规划
class Solution:
    def translateNum(self, num: int) -> int:
        num = str(num)
        n = len(num)
        if n <= 1:
            return 1
        dp = [1, 1]
        i = 1
        while i < n:
            if num[i - 1] == '1' or (num[i - 1] == '2' and num[i] in "012345"):
                tmp = dp[0] + dp[1]
            else:
                tmp = dp[1]
            dp[0] = dp[1]
            dp[1] = tmp
            i += 1
        return dp[-1]
# TODO: 减少时间复杂度