443. String Compression

#### QUESTION:

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:

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

#### SOLUTION:

``````class Solution {
public int compress(char[] chars) {
if(chars.length==0) return 0;
int count = 1;
char pre = chars;
StringBuilder sb = new StringBuilder();
for(int i = 1;i<chars.length;i++){
if(chars[i]==pre){
count++;
}else{
sb.append(pre);
if(count>1) sb.append(count);
pre = chars[i];
count = 1;
}
}
sb.append(pre);
if(count>1) sb.append(count);
char[] res = sb.toString().toCharArray();
for(int i =0;i<res.length;i++) chars[i] = res[i];
return res.length;
}
}
``````
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