[leetCode] 443. String Compression (Python)

Given an array of characters, compress it in-place.

The length after compression must always be smaller than or equal to the original array.

Every element of the array should be a character (not int) of length 1.

After you are done modifying the input array in-place, return the new length of the array.

 

Follow up:
Could you solve it using only O(1) extra space?

 

Example 1:

Input:
["a","a","b","b","c","c","c"]

Output:
Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]

Explanation:
"aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".

 

Example 2:

Input:
["a"]

Output:
Return 1, and the first 1 characters of the input array should be: ["a"]

Explanation:
Nothing is replaced.

 

Example 3:

Input:
["a","b","b","b","b","b","b","b","b","b","b","b","b"]

Output:
Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].

Explanation:
Since the character "a" does not repeat, it is not compressed. "bbbbbbbbbbbb" is replaced by "b12".
Notice each digit has it's own entry in the array.

 

Note:

1. All characters have an ASCII value in [35, 126].
2. 1 <= len(chars) <= 1000.

Solution

class Solution:
    def compress(self, chars: List[str]) -> int:
        stack = []
        nums = 1
        idx = 0
        
        if len(chars) > 0:
            stack.append(chars[0])
        
        for i in range(1, len(chars)):
            if chars[i] == stack[idx]:
                nums = nums + 1
                
                if i == len(chars) - 1:
                    num_list = list(str(nums))
                    idx = idx + 1 + len(num_list)
                
                    stack = stack + num_list
                    
                
            elif chars[i] != stack[idx]:

                if nums == 1:    
                    idx = idx + 1

                num_list = list(str(nums))
                
                if num_list != ['1']:
                    idx = idx + 1 + len(num_list)
                    stack = stack + num_list
                
                stack.append(chars[i])
                nums = 1

        for i in range(len(stack)):
            chars[i] = stack[i]
        
        chars = chars[0:len(stack)]
        
        return len(chars)

SOMJANG/CODINGTEST_PRACTICE