crack the coding interview 数组与字符串 1.5

crack the coding interview 数组与字符串 1.5

package ac.crack_code_interview.ch01_array_string;

import org.junit.Test;

/**
* description:
*
* @author liyazhou
* @since 2017-06-27 10:45
* 9.1 数组与字符串
*
* 题目 1.5
*      利用字符串重复出现的次数，编写一个方法，实现基本的字符串压缩功能。
*      比如，字符串 aabcccccaaa 会变成 a2b1c5a3。
*      若“压缩”后的字符串没有变短，则返回原先的字符串。
*
* 思路
*      1. 先遍历字符串，计算压缩后的空间大小
*
*/
public class Test05 {

// 是否可用 StringBuilder 类
public String compress2(String str){
if (str == null) return null;

StringBuilder sBuilder = new StringBuilder();
char currChar = str.charAt(0);
int counter = 1;
for (int i = 1; i < str.length(); i ++){
if (str.charAt(i) == currChar) counter ++;
else {
sBuilder.append(currChar).append(counter);

currChar = str.charAt(i);
counter = 1;
}
}
sBuilder.append(currChar).append(counter);

return sBuilder.length() < str.length() ? sBuilder.toString() : str;
}

public char[] compress(char[] chars){
if (chars == null) return chars;
int newLen = calculateLen(chars);
if (newLen > chars.length) return chars;

char[] compressedChars = new char[newLen];
int newIdx = 0;
char currChar = chars[0];
int counter = 1;
for (int i = 1; i < chars.length; i ++){
if (chars[i] == currChar) counter ++;
else {
compressedChars[newIdx++] = currChar;
String str = String.valueOf(counter);
for (int j = 0; j < str.length(); j ++)
compressedChars[newIdx++] = str.charAt(j);

currChar = chars[i];
counter = 1;
}
}
compressedChars[newIdx++] = currChar;
String str = String.valueOf(counter);
for (int j = 0; j < str.length(); j ++)
compressedChars[newIdx++] = str.charAt(j);

return compressedChars;
}

private int calculateLen(char[] chars) {
int total = 0;
char currChar = chars[0];
int counter = 1;
for (int i = 1; i < chars.length; i ++){
if (chars[i] == currChar) counter ++;
else{
total ++;  // 当前字符占一个位置
total += String.valueOf(counter).length(); // 当前字符重复的次数是几位数字，则占几位

currChar = chars[i];
counter = 1;
}
}
total ++;
total += String.valueOf(counter).length();

return total;
}

@Test
public void test(){
String[] strs = {
"aaabbbcccddd",
"abcdefghijklmn"
};
for (String str : strs){
System.out.println(str);
char[] result = compress(str.toCharArray());
System.out.println(new String(result));
System.out.println(compress2(str));
System.out.println();
}
}
}