18-String-Compression.md

String Compression

Problem Link

https://leetcode.com/problems/string-compression/

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Pattern

• String

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Approach

Use write pointer to compress in-place. Count consecutive characters and update chars array.

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Time Complexity

O(n)

Space Complexity

O(1)

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Java Solution

class Solution {
    public int compress(char[] chars) {
        int write = 0;
        for (int i = 0; i < chars.length; ) {
            char c = chars[i];
            int count = 0;
            while (i < chars.length && chars[i] == c) {
                count++;
                i++;
            }
            chars[write++] = c;
            if (count > 1) {
                for (char d : String.valueOf(count).toCharArray()) {
                    chars[write++] = d;
                }
            }
        }
        return write;
    }
}