C#LeetCode刷题之#443-压缩字符串​​​​​​​（String Compression）

• 所有字符都有一个ASCII值在[35, 126]区间内。
• 1 <= len(chars) <= 1000。

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?

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”.

Input:[‘a’]

Output:Return 1, and the first 1 characters of the input array should be: [‘a’]

Explanation:Nothing is replaced.

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:

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

```public class Program {

public static void Main(string[] args) {
var chars = new char[] { 'a', 'b', 'b' };

var res = Compress(chars);
Console.WriteLine(res);

chars = new char[] { 'a', 'a', 'b', 'b', 'c', 'c', 'c' };

res = Compress2(chars);
Console.WriteLine(res);

}

private static int Compress(char[] chars) {
if(chars.Length == 1) return 1;
var count = 1;
var res = string.Empty;
for(var i = 1; i < chars.Length; i++) {
if(chars[i] == chars[i - 1]) {
count++;
} else {
res += chars[i - 1].ToString() + (count == 1 ? "" : count.ToString());
count = 1;
}
if(i == chars.Length - 1) res +=
chars[i].ToString() + (count == 1 ? "" : count.ToString());
}
for(int i = 0; i < res.Length; i++) {
chars[i] = res[i];
}
return res.Length;
}

private static int Compress2(char[] chars) {
if(chars.Length == 1) return 1;
var index = 0;
var count = 1;
for(var i = 1; i < chars.Length; i++) {
if(chars[i] == chars[i - 1]) {
count++;
} else {
ResetChars(chars, ref count, ref index, i - 1);
}
if(i == chars.Length - 1) {
ResetChars(chars, ref count, ref index, i);
}
}
return index;
}

private static void ResetChars(char[] chars, ref int count, ref int index, int i) {
if(count != 1) {
chars[index] = chars[i];
for(int j = 0; j < count.ToString().Length; j++) {
chars[j + index + 1] = count.ToString()[j];
}
index += count.ToString().Length + 1;
} else {
chars[index] = chars[i];
index++;
}
count = 1;
}

}```

```3
6```

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