Run Length Encoding
static String decoding(String s) {
int count = 0;
StringBuilder ret = new StringBuilder();
for (char c : s.toCharArray()) {
if (Character.isDigit(c)) {
count = count * 10 + c - '0';
} else { // isalpha.
for (int i = 1; i <= count; i++) {
ret.append(c);
}
count = 0;
}
}
return ret.toString();
}
static String encoding(String s) {
int count = 1;
StringBuilder ss = new StringBuilder();
for (int i = 1; i < s.length(); ++i) {
if (s.charAt(i) == s.charAt(i - 1)) {
++count;
} else {
ss.append(count);
ss.append(s.charAt(i - 1));
count = 1;
}
}
ss.append(count);
ss.append(s.charAt(s.length() - 1));
return ss.toString();
}
Remove b and Replace b with dd
Main idea is to process backward
static String replaceAndRemove(String s) {
char[] sChars = s.toCharArray();
// Removes "b" and count the number of "a".
int writeIdx = 0, aCount = 0;
for (char c : sChars) {
if (c != 'b') {
sChars[writeIdx++] = c;
}
if (c == 'a') {
++aCount;
}
}
// Allocates space according to the number of "a".
sChars = Arrays.copyOf(sChars, writeIdx + aCount);
// Replace "a" with "dd".
int curIdx = writeIdx - 1;
writeIdx = sChars.length - 1;
while (curIdx >= 0) {
if (sChars[curIdx] == 'a') {
sChars[writeIdx--] = 'd';
sChars[writeIdx--] = 'd';
} else {
sChars[writeIdx--] = sChars[curIdx];
}
--curIdx;
}
return new String(sChars);
}
PhoneMnemonic
static void phoneMnemonicHelper(String num, int d, char[] ans) {
if (d == num.length()) { // get enough characters and output answer.
System.out.println(ans);
} else {
for (char c : M[num.charAt(d) - '0'].toCharArray()) { // try all
// combinations.
ans[d] = c;
phoneMnemonicHelper(num, d + 1, ans);
}
}
}
static void phoneMnemonic(String num) {
char[] ans = new char[num.length()];
phoneMnemonicHelper(num, 0, ans);
}
