Leetcode 394 Solution

This article provides solution to leetcode question 394 (decode-string)
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https://leetcode.com/problems/decode-string

Solution

class Solution:
    def decodeString(self, s: str) -> str:
        i = 0

        def decode():
            nonlocal s
            nonlocal i

            if i == len(s):
                return ""

            ans = ""

            while i < len(s):
                if 'a' <= s[i] <= 'z':
                    ans += s[i]
                    i += 1
                elif '0' <= s[i] <= '9':
                    val = 0

                    while s[i] != '[':
                        val = val * 10 + int(s[i])
                        i += 1

                    i += 1

                    substr = decode()
                    ans += substr * val
                elif s[i] == ']':
                    i += 1
                    break
                else:
                    raise Exception("Unexpected char '{}'!".format(s[i]))

            return ans

        return decode()