StringCompression443.java

/**
 * 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.
 */


public class StringCompression443 {
 public int compress(char[] chars) {
 if (chars == null || chars.length <= 0) return 0;
 if (chars.length == 1) return 1;
 int i = 1;
 int j = 1;
 int count = 1;
 char pre = chars[0];
 while (j < chars.length) {
 if (chars[j] == pre) {
 count++;
 j++;
 } else {
 if (count != 1) {
 char[] nums = Integer.toString(count).toCharArray();
 for (char n: nums) {
 chars[i++] = n;
 }
 }
 pre = chars[j];
 count = 1;
 j++;
 chars[i] = pre;
 i++;
 }
 }
 if (count != 1) {
 char[] nums = Integer.toString(count).toCharArray();
 for (char n: nums) {
 chars[i++] = n;
 }
 }
 return i;
 }


 /**
 * https://leetcode.com/problems/string-compression/solution/
 */
 public int compress2(char[] chars) {
 int anchor = 0, write = 0;
 for (int read = 0; read < chars.length; read++) {
 if (read + 1 == chars.length || chars[read + 1] != chars[read]) {
 chars[write++] = chars[anchor];
 if (read > anchor) {
 for (char c: ("" + (read - anchor + 1)).toCharArray()) {
 chars[write++] = c;
 }
 }
 anchor = read + 1;
 }
 }
 return write;
 }

}