I'm trying to solve simple Java problems in various ways. Could anyone comment about the code, like how it could be better, and what could be a problem?
// When using already-defined-method is allowed
static String reverseStringByChar1(String str) {
return str == null ? null : new StringBuilder(str).reverse().toString();
}
// When using already-defined-method is not allowed
static String reverseStringByChar2(String str) {
if (str == null)
return null;
int length = str.length();
char[] charArray = new char[length];
for (int i = length-1, j = 0; i >= 0; i--, j++)
charArray[i] = str.charAt(j);
return new String(charArray);
}
// When using extra data structure is not allowed
// (Is there any way not to use extra memory? Here like the temp.)
static String reverseCharacterArray(char[] chars) {
if(chars.length == 0)
return null;
for (int i = 0, j = chars.length-1; i < chars.length / 2; i++, j--) {
/* char temp = chars[i];
chars[i] = chars[j];
chars[j] = temp;
*/
char temp = chars[i];
chars[i] = chars[chars.length-1-i];
chars[chars.length-1-i] = temp;
}
return new String(chars);
}
// When comparing two strings to see if they are permutations of each other.
static boolean arePermutations(String str1, String str2) {
// can be trimmed
// need to know what to do with uppercases and lowercase
if (str1 == null || str2 == null || str1.length() != str2.length())
return false;
// assuming askii code
boolean[] str1Array = new boolean[128];
for (char c : str1.toCharArray())
str1Array[c] = true;
for (char c : str2.toCharArray()) {
if (!str1Array[c])
return false;
}
return true;
}
