decode_string_iterative

# Time Complexity : O(OUTPUT)
# Space Complexity : O(OUTPUT)
# Did this code successfully run on Leetcode : Yes
# Any problem you faced while coding this : No

class Solution:
    def decodeString(self, s: str) -> str:
        numStk = []
        strStk = []
        num = 0
        currStr = ""
        i = 0
        while i < len(s): 
            if s[i].isdigit():
                num = num * 10 + int(s[i])
                i += 1
            elif s[i] == "[":
                numStk.append(num)
                strStk.append(currStr)
                i += 1
                num = 0
                currStr = ""
                
            elif s[i] == "]":
                multiplyer = numStk.pop()
                parentStr = strStk.pop()
                tempStr = currStr *  multiplyer
                currStr = parentStr+tempStr
                i += 1
                
            elif s[i].isalpha():
                currStr = currStr + s[i]
                i += 1
                
        return currStr