443. String Compression(easy)

Easy

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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.

 

借助辅助向量法:

c++:

/*
 * @Autor: SourDumplings
 * @Date: 2019-09-25 19:52:39
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/string-compression/
 */

class Solution
{
public:
    int compress(vector<char> &chars)
    {
        int count = 0;
        vector<char> res;
        char lastChar = 0;
        for (char c : chars)
        {
            if (c == lastChar)
            {
                ++count;
            }
            else
            {
                if (count == 1)
                {
                    res.push_back(lastChar);
                }
                else if (count > 1)
                {
                    res.push_back(lastChar);
                    string num = to_string(count);
                    for (auto &&cn : num)
                    {
                        res.push_back(cn);
                    }
                }
                count = 1;
                lastChar = c;
            }
        }
        if (count == 1)
        {
            res.push_back(lastChar);
        }
        else if (count > 1)
        {
            res.push_back(lastChar);
            string num = to_string(count);
            for (auto &&cn : num)
            {
                res.push_back(cn);
            }
        }
        chars = std::move(res);
        return chars.size();
    }
};

Java：

import java.util.ArrayList;
import java.util.List;

/*
 * @Autor: SourDumplings
 * @Date: 2019-09-25 20:10:59
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/string-compression/
 */

class Solution
{
    private int count = 0;
    private char lastChar = (char) 0;

    public int compress(char[] chars)
    {
        List<Character> res = new ArrayList<>();
        for (char c : chars)
        {
            if (c == lastChar)
            {
                ++count;
            }
            else
            {
                record(lastChar, res);
                count = 1;
                lastChar = c;
            }
        }
        record(lastChar, res);
        int l = res.size();
        int i = 0;
        for (char c : res)
        {
            chars[i++] = c;
        }
        return l;
    }

    void record(char c, List<Character> res)
    {
        if (count == 1)
        {
            res.add(c);
        }
        else if (count > 1)
        {
            res.add(c);
            String num = String.valueOf(count);
            int l = num.length();
            for (int i = 0; i < l; i++)
            {
                char d = num.charAt(i);
                res.add(d);
            }
        }
    }
}

 就地法：

Java：

/*
 * @Autor: SourDumplings
 * @Date: 2019-09-25 20:36:42
 * @Link: https://github.com/SourDumplings/
 * @Email: changzheng300@foxmail.com
 * @Description: https://leetcode.com/problems/string-compression/
 */

class Solution
{
    public int compress(char[] chars)
    {
        int count = 0;
        char lastChar = (char) 0;
        int i = 0;
        for (char c : chars)
        {
            if (c == lastChar)
            {
                ++count;
            }
            else
            {
                if (count == 1)
                {
                    chars[i++] = lastChar;
                }
                else if (count > 1)
                {
                    chars[i++] = lastChar;
                    String num = String.valueOf(count);
                    int l = num.length();
                    for (int j = 0; j < l; j++)
                    {
                        char d = num.charAt(j);
                        chars[i++] = d;
                    }
                }
                count = 1;
                lastChar = c;
            }
        }
        if (count == 1)
        {
            chars[i++] = lastChar;
        }
        else if (count > 1)
        {
            chars[i++] = lastChar;
            String num = String.valueOf(count);
            int l = num.length();
            for (int j = 0; j < l; j++)
            {
                char d = num.charAt(j);
                chars[i++] = d;
            }
        }
        return i;
    }
}