Formatted question description: https://leetcode.ca/all/443.html

443. String Compression (Easy)

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.

Companies:
Microsoft, Goldman Sachs, Bloomberg

Related Topics:
String

Similar Questions:

Solution 1.

// OJ: https://leetcode.com/problems/string-compression/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    int compress(vector<char>& chars) {
        int i = 0, N = chars.size(), j = 0, r = 0;
        while (i < N) {
            j = i + 1;
            while (j < N && chars[j] == chars[i]) ++j;
            chars[r++] = chars[i];
            if (j - i > 1) {
                int cnt = j - i, pow = 1;
                while (cnt / (pow * 10)) pow *= 10;
                while (pow) {
                    chars[r++] = '0' + cnt / pow;
                    cnt %= pow;
                    pow /= 10;
                }
            }
            i = j;
        }
        return r;
    }
};

Java

class Solution {
    public int compress(char[] chars) {
        if (chars == null)
            return 0;
        int length = chars.length;
        if (length <= 1)
            return length;
        int index = 0;
        char prevChar = chars[0];
        int count = 1;
        for (int i = 1; i < length; i++) {
            char c = chars[i];
            if (c == prevChar)
                count++;
            else {
                chars[index] = prevChar;
                index++;
                if (count > 1) {
                    String countStr = String.valueOf(count);
                    int countLength = countStr.length();
                    for (int j = 0; j < countLength; j++) {
                        chars[index] = countStr.charAt(j);
                        index++;
                    }
                    count = 1;
                }
                prevChar = c;
            }
        }
        if (count > 0) {
            chars[index] = prevChar;
            index++;
            if (count > 1) {
                String countStr = String.valueOf(count);
                int countLength = countStr.length();
                for (int j = 0; j < countLength; j++) {
                    chars[index] = countStr.charAt(j);
                    index++;
                }
            }
        }
        return index;
    }
}

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