140.String Compression

题目：

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

给定一组字符，就地压缩它。

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

压缩后的长度必须始终小于或等于原始数组。

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

数组的每个元素都应该是长度为1的字符（不是int）。

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

在就地修改输入数组后，返回数组的新长度。

Follow up:

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

你能用O（1）额外空间解决它吗？

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"]
返回6，输入数组的前6个字符应为：[“a”，“2”，“b”，“2”，“c”，“3”]

Explanation:
"aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".
“aa”被“a2”取代。 “bb”被“b2”取代。 “ccc”被“c3”取代。

 

Example 2:

Input:
["a"]

Output:
Return 1, and the first 1 characters of the input array should be: ["a"]
返回1，输入数组的前1个字符应为：[“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"].
返回4，输入数组的前4个字符应为：[“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.
由于字符“a”不重复，因此不会压缩。 “bbbbbbbbbbbbb”被“b12”取代。
请注意，每个数字在数组中都有自己的条目。

 

Note:

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

 

解答：

class Solution {
    public int compress(char[] chars) {
        int slow=0,fast=0;
        while(fast<chars.length){
            char currChar=chars[fast];
            int count=0;
            while(fast<chars.length && chars[fast]==currChar){
                fast++;
                count++;
            }
            chars[slow++]=currChar;
            if(count!=1)
                for(char c:Integer.toString(count).toCharArray())
                    chars[slow++]=c;
        }
        return slow;
    }
}

详解：

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