443. String Compression

• Difficulty: Easy

• Topics: String

• Similar Questions:

  • Count and Say

  • Encode and Decode Strings

  • Design Compressed String Iterator

Problem:

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.

Solutions:

class Solution {
public:
    int compress(vector<char>& chars) {
        if (chars.size() == 0)    return 0;

        int pos = 0;
        int index = 0;
        char c;
        int count;
        while (index < chars.size()) {
            c = chars[index++];
            count = 1;
            while (index < chars.size() && chars[index] == c) {
                ++index;
                ++count;
            }
            if (count == 1) {
                chars[pos++] = c;
            } else {
                chars[pos++] = c;
                string countStr = to_string(count);
                for (auto& v : countStr) {
                    chars[pos++] = v;
                }
            }
        }

        return pos;
    }
};