String Compression Leetcode


#1

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.

#2

The below algorithm checks for consecutive characters which are similar. If there are more than one, then we use a temp index to remember where we left the assignment last time.

func compress(chars []byte) int {
    var ti int
    for i:=0;i<len(chars);i++{
        ch := chars[i]
        count := 1
        for i<len(chars)-1 && chars[i]==chars[i+1] {
            count++
            i++
        }
        if count>1{
            chars[ti]=ch
            ti++
            if count<9 {
                 chars[ti] = byte(count)+'0'
                 ti++
            } else {
                sb := convertToByteArr(count)
                for j:=len(sb)-1;j>=0;j-- {
                    chars[ti] = sb[j]
                    ti++
                }
            }
           
        } else {
            chars[ti]=ch
            ti++
        }
    }
    
    return ti
}

func convertToByteArr(val int) string {
    var sb strings.Builder
    for val!=0{
        sb.WriteByte(byte(val%10)+'0')
        val = val/10
    }
    return sb.String()
}