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17.java
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17.java
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0ms
class Solution {
private static final String[] KEYS = {"","","abc","def","ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
public List<String> letterCombinations(String digits) {
List<String> ret = new LinkedList<>();
if (digits == null || digits.length() < 1) {
return ret;
}
combination("",digits,0,ret);
return ret;
}
public void combination(String prefix, String digits, int offset, List<String> ret) {
if (offset >= digits.length()) {
ret.add(prefix);
return;
}
String letters = KEYS[ digits.charAt(offset) - '0' ];
for (int i=0; i<letters.length(); i++) {
combination(prefix+letters.charAt(i), digits, offset+1, ret);
}
}
}
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1ms
class Solution {
List<String> ans = new ArrayList<>();
Map<String, List<String>> map = new HashMap<String, List<String>>() {{
put("2", Arrays.asList("a", "b", "c"));
put("3", Arrays.asList("d", "e", "f"));
put("4", Arrays.asList("g", "h", "i"));
put("5", Arrays.asList("j", "k", "l"));
put("6", Arrays.asList("m", "n", "o"));
put("7", Arrays.asList("p", "q", "r", "s"));
put("8", Arrays.asList("t", "u", "v"));
put("9", Arrays.asList("w", "x", "y", "z"));
}};
public List<String> letterCombinations(String digits) {
if (digits.length() == 0) {
return ans;
}
letterCombinationHelper(digits, "", 0);
return ans;
}
private void letterCombinationHelper(String digits, String s, int i) {
if (i == digits.length()) {
ans.add(s);
return;
}
for (String t : map.get(digits.substring(i, i + 1))) {
letterCombinationHelper(digits, s + t, i + 1);
}
}
}
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2ms
class Solution {
private final Map<Character, List<Character>> intCharMap;
public Solution () {
intCharMap = new HashMap<>(10);
intCharMap.put('2', Arrays.asList(new Character[]{'a', 'b', 'c'}));
intCharMap.put('3', Arrays.asList(new Character[]{'d', 'e', 'f'}));
intCharMap.put('4', Arrays.asList(new Character[]{'g', 'h', 'i'}));
intCharMap.put('5', Arrays.asList(new Character[]{'j', 'k', 'l'}));
intCharMap.put('6', Arrays.asList(new Character[]{'m', 'n', 'o'}));
intCharMap.put('7', Arrays.asList(new Character[]{'p', 'q', 'r', 's'}));
intCharMap.put('8', Arrays.asList(new Character[]{'t', 'u', 'v'}));
intCharMap.put('9', Arrays.asList(new Character[]{'w', 'x', 'y', 'z'}));
}
public List<String> letterCombinations(String digits) {
Map<Integer, List<Character>> digitsLookedUp = new HashMap<>();
for (int i=0; i<digits.length(); i++) {
digitsLookedUp.put(i, intCharMap.get(digits.charAt(i)));
}
int lengthOfWord = digitsLookedUp.size();
List<String> toReturn = new ArrayList<>();
for (int i=0; i<lengthOfWord; i++) {
List<Character> chars = digitsLookedUp.get(i);
if (toReturn.size()==0) {
for(char c : chars) {
toReturn.add(String.valueOf(c));
}
} else {
List<String> toTempReturn = new ArrayList<>();
for (String s : toReturn) {
for (Character c : chars) {
toTempReturn.add(s + c);
}
}
toReturn = toTempReturn;
}
}
return toReturn;
}
}
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34516 kb
class Solution {
Map<Character, String> phone = new HashMap<Character, String>() {{
put('2', "abc");
put('3', "def");
put('4', "ghi");
put('5', "jkl");
put('6', "mno");
put('7', "pqrs");
put('8', "tuv");
put('9', "wxyz");
}};
List<String> output;
public void backtrack(String combination, String next_digits){
// if there is no more digits to check
if(next_digits.length() == 0){
// the combination is done
output.add(combination);
}
// if there are still digits to check
else {
// iterate over all letters which map
// the next available digit
char digit = next_digits.charAt(0);
String letters = phone.get(digit);
for(int i = 0 ; i < letters.length() ; i++){
char letter = phone.get(digit).charAt(i);
// append the current letter to the combination
// and proceed to the next digits
backtrack(combination + letter, next_digits.substring(1));
}
}
}
public List<String> letterCombinations(String digits) {
output = new ArrayList<>();
if(digits.length() != 0){
backtrack("", digits);
}
return output;
}
}
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34548 kb
class Solution {
private String[] mapping = new String[] {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
public List<String> letterCombinations(String digits) {
LinkedList<String> ans = new LinkedList<String>();
if(digits.length() == 0) return ans;
helper(ans, digits, "", 0);
return ans;
}
public void helper(List<String> ans, String digits, String cur, int count){
if(count == digits.length()){
ans.add(cur);
return;
}
String temp = new String(cur);
for(char c : mapping[digits.charAt(count)-'0'].toCharArray()){
helper(ans, digits, cur+c, count+1);
cur = temp;
}
}
}
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