Facebook Interview Question
SDE1sCountry: United States
1. Use a hashmap to store the Character Count.
2. Then iterate through the char array again, and keep track of the last character used.
3. Remove the entries from hashmap when the count becomes 0.
public static int getJob(char[] arr, int k){
if(arr.length == 0){
return 0;
}
HashMap<Character, Integer> map = new HashMap<>();
for(int i=0; i<arr.length; i++){
if(map.containsKey(arr[i]))
map.put(arr[i], map.get(arr[i])+ 1);
else
map.put(arr[i], 1);
}
int res = 0;
char l = ' ';
int i = 0;
while(!map.isEmpty()){
if(i == arr.length){
i = 0;
}
if(arr[i] == ' '){
i++;
continue;
}
else if(arr[i] != l){
res +=1;
map.put(arr[i], map.get(arr[i])-1);
if(map.get(arr[i]) == 0){
map.remove(arr[i]);
}
l = arr[i];
arr[i] = ' ';
i++;
}
else if(map.size() == 1){
int val = map.get(arr[i]);
res += val * k + val;
map.remove(arr[i]);
i++;
}else
i++;
}
return res;
}
public static void main(String[] args){
char[] arr1 = {'A','A','A','B','B','B','C','C','C'};
char[] arr2 = {'A','A','A','B','C'};
System.out.println(getJob(arr1, 3));
System.out.println(getJob(arr2, 2));
}
public static int reArrangeTasks(String tasks,int coolDown){
Map<Character,Integer> map=new HashMap<Character, Integer>();
//Storing string in may by character as key and number of repetions of it as value
for(int i=0;i<tasks.length();i++){
char c=tasks.charAt(i);
if(map.containsKey(c)){
map.put(c, map.get(c)+1);
}
else{
map.put(c, 1);
}
}
//looping through map and removing each character in every unique alphabet for cooltime period
int c=0;
boolean newLoop=false;
while(!map.isEmpty()){
newLoop=true;
Iterator<Character> it=map.keySet().iterator();
while(it.hasNext()){
char ch=it.next();
if(!newLoop && c!=0 && c%(coolDown+1)==0) break;
newLoop=false;
map.put(ch, map.get(ch)-1);
c++;
if(map.get(ch)==0) it.remove();
}
while(c%(coolDown+1)!=0 && !map.isEmpty()) c++;
}
return c;
}
public static int reArrangeTasks(String tasks,int coolDown){
Map<Character,Integer> map=new HashMap<Character, Integer>();
//Storing string in may by character as key and number of repetions of it as value
for(int i=0;i<tasks.length();i++){
char c=tasks.charAt(i);
if(map.containsKey(c)){
map.put(c, map.get(c)+1);
}
else{
map.put(c, 1);
}
}
//looping through map and removing each character in every unique alphabet for cooltime period
int c=0;
boolean newLoop=false;
while(!map.isEmpty()){
newLoop=true;
Iterator<Character> it=map.keySet().iterator();
while(it.hasNext()){
char ch=it.next();
if(!newLoop && c!=0 && c%(coolDown+1)==0) break;
newLoop=false;
map.put(ch, map.get(ch)-1);
c++;
if(map.get(ch)==0) it.remove();
}
while(c%(coolDown+1)!=0 && !map.isEmpty()) c++;
}
return c;
}
string OptimizeTasks(string const &tasks)
{
unordered_map<char, int> task_count;
for (char c : tasks) {
++task_count[c];
}
string optimized;
while (!task_count.empty()) {
for (auto it = task_count.begin(); it != task_count.end(); ++it) {
optimized += it->first;
if (--it->second == 0) {
task_count.erase(it->first);
}
}
}
return optimized;
}
//C# Code working for me
//optTaskSeqK("AAABBBCCC", 3);
private static Tuple<string, int> optTaskSeqK(string tasks, int coolTime)
{
var taskGp = tasks.GroupBy(s => s).Select(s => new { task = s.Key, count = s.Count() });
var taskDic = taskGp.ToDictionary(g => g.task, g => g.count);
var recTaskDic = taskGp.ToDictionary(g => g.task, g => 0);
var coolTaskDic = taskGp.ToDictionary(g => g.task, g => 0);
String taskOrder = string.Empty;
int totalExeTime = 0;
optTask cuTask = new optTask();
//int cuTaskExeTime=0;
for (int seq = 0; seq < tasks.Length; seq++)
{
foreach (var key in recTaskDic.Keys)
{
if (coolTaskDic[key] != 0)
coolTaskDic[key] -= 1;
}
cuTask = getNextOptTask(seq);
totalExeTime += 1 + coolTaskDic[cuTask.taskCh];
coolTaskDic[cuTask.taskCh] += coolTime;
taskOrder += cuTask.taskCh;
}
optTask getNextOptTask(int seq)
{
var taskGP = taskDic.Where(i => i.Value > 0).GroupBy(i => i.Value).OrderByDescending(i => i.Key).First().ToList();
//if (taskGp.Count() == 1)
// return taskGP.First().Key;
var optTask = new optTask { taskCh = '\0', exeTime = int.MaxValue, seq = int.MaxValue };
var tempTask = new optTask();
foreach (var ti in taskDic)
{
if (ti.Value > 0)
{
tempTask = new optTask();
tempTask.taskCh = ti.Key;
tempTask.count = ti.Value;
tempTask.seq = recTaskDic[ti.Key];
tempTask.exeTime = 1 + coolTaskDic[ti.Key];
optTask = compOptTask(tempTask, optTask);
}
}
taskDic[optTask.taskCh]--;
recTaskDic[optTask.taskCh] = seq;
return optTask;
};
optTask compOptTask(optTask t1, optTask t2)
{
if (t1.exeTime != t2.exeTime)
return t1.exeTime < t2.exeTime ? t1 : t2;
if (t1.count != t2.count)
return t1.count > t2.count ? t1 : t2;
if (t1.seq != t2.seq)
return t1.seq < t2.seq ? t1 : t2;
return t2;
}
return Tuple.Create(taskOrder, totalExeTime);
}
class optTask
{
public char taskCh;
public int exeTime;
public int count { get; set; }
public int seq { get; set; }
}
Example 1 (k=3, ie distance should be 3 in between same tasks) does not match with examples 2 & 3
test runs:
t.rearrangeTasks("AAABBBCCC", 3); => ABC_ABC_ABC 11
t.rearrangeTasks("AAABC", 2); => ABCA__A 7
t.rearrangeTasks("AAADBBCC", 2); => ABCADBAC 8
t.rearrangeTasks("AAADBBC", 2); => ABCABDA 7
t.rearrangeTasks("CCCBBB", 2); => BC_BC_BC 8
t.rearrangeTasks("CCCBBB", 3); => BC__BC__BC 10
t.rearrangeTasks("AAAAAABBCCCCCDDDD", 2); => ABCADCADCABCADCAD 17
t.rearrangeTasks("AAAAAAAAAABBCCCCCDDDD", 2); => ABCAD_AC_A_DA_CA_BAC_AD_ADCA 28
public int rearrangeTasks(String tasks, int cooldown){
HashMap<Character, Integer> occurMap = new HashMap<>();
//compute map
for (int i=0; i < tasks.length();i++) {
char c = tasks.charAt(i);
Integer occurence = occurMap.get(c);
if (occurence == null) {
occurMap.put(c, 1);
} else {
occurMap.put(c, occurence+1);
}
}
HashMap<Character, Integer> distMap = new HashMap<>();
final AtomicInteger startPos = new AtomicInteger(0);
AtomicInteger minDist = new AtomicInteger(tasks.length());
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
//placing same tasks far apart within minDist
int charDist = minDist.get() / occurence;
if (charDist <= cooldown) {
int newCharDist = (cooldown + 1);
distMap.put(c, newCharDist);
int newDist = (occurence-1) * newCharDist +
startPos.incrementAndGet();
if (minDist.get() < newDist) {
minDist.set(newDist);
}
} else {
distMap.put(c, charDist);
}
});
//only to print output task order, not required otherwse
AtomicInteger writePos = new AtomicInteger(-1);
char[] out = new char[minDist.get()];
Arrays.fill(out, '_');
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
int pos = writePos.incrementAndGet();
int charDist = distMap.get(c);
while(occurence > 0) {
while (out[pos] != '_' ||
anyInRange(out, pos-cooldown, pos+cooldown, c)) {
pos += (charDist + 1); //conflicts, moveover
pos %= minDist.get();
}
out[pos] = c;
occurence--;
pos += (charDist);
pos %= minDist.get();
}
});
System.out.println(new String(out) + " " + out.length);
return minDist.get();
}
private boolean anyInRange(char[] out, int i, int j, char c) {
if (i < 0) {
i = 0;
}
if (j >= out.length) {
j = out.length - 1;
}
for (int k = i; k <= j; k++) {
if (out[k] == c) {
return true;
}
}
return false;
}
Output:
ABC_ABC_ABC 11
ABCDEABCDEABCDEABCDEABCDE 25
ABCA__A 7
ABCADBAC 8
ABCABDA 7
BC_BC_BC 8
BC__BC__BC 10
ABCADCADCABCADCAD 17
ABCAD_AC_A_DA_CA_BAC_AD_ADCA 28
public class TaskDistance {
public static void main(String[] args) {
TaskDistance t = new TaskDistance();
t.rearrangeTasks("AAABBBCCC", 3);
t.rearrangeTasks("AAAAABBBBBCCCCCDDDDDEEEEE", 3);
t.rearrangeTasks("AAABC", 2);
t.rearrangeTasks("AAADBBCC", 2);
t.rearrangeTasks("AAADBBC", 2);
t.rearrangeTasks("CCCBBB", 2);
t.rearrangeTasks("CCCBBB", 3);
t.rearrangeTasks("AAAAAABBCCCCCDDDD", 2);
t.rearrangeTasks("AAAAAAAAAABBCCCCCDDDD", 2);
}
public int rearrangeTasks(String tasks, int cooldown){
HashMap<Character, Integer> occurMap = new HashMap<>();
//compute map
for (int i=0; i < tasks.length();i++) {
char c = tasks.charAt(i);
Integer occurence = occurMap.get(c);
if (occurence == null) {
occurMap.put(c, 1);
} else {
occurMap.put(c, occurence+1);
}
}
HashMap<Character, Integer> distMap = new HashMap<>();
final AtomicInteger startPos = new AtomicInteger(0);
AtomicInteger minDist = new AtomicInteger(tasks.length());
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
//placing same tasks far apart within minDist
int charDist = minDist.get() / occurence;
if (charDist <= cooldown) {
int newCharDist = (cooldown + 1);
distMap.put(c, newCharDist);
int newDist = (occurence-1) * newCharDist +
startPos.incrementAndGet();
if (minDist.get() < newDist) {
minDist.set(newDist);
}
} else {
distMap.put(c, charDist);
}
});
//only to print output task order, not required otherwse
AtomicInteger writePos = new AtomicInteger(-1);
char[] out = new char[minDist.get()];
Arrays.fill(out, '_');
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
int pos = writePos.incrementAndGet();
int charDist = distMap.get(c);
while(occurence > 0) {
while (out[pos] != '_' ||
anyInRange(out, pos-cooldown, pos+cooldown, c)) {
pos += (charDist + 1); //conflicts, moveover
pos %= minDist.get();
}
out[pos] = c;
occurence--;
pos += (charDist);
pos %= minDist.get();
}
});
System.out.println(new String(out) + " " + out.length);
return minDist.get();
}
private boolean anyInRange(char[] out, int i, int j, char c) {
if (i < 0) {
i = 0;
}
if (j >= out.length) {
j = out.length - 1;
}
for (int k = i; k <= j; k++) {
if (out[k] == c) {
return true;
}
}
return false;
}
}
public class TaskDistance {
public static void main(String[] args) {
TaskDistance t = new TaskDistance();
t.rearrangeTasks("AAABBBCCC", 3);
t.rearrangeTasks("AAAAABBBBBCCCCCDDDDDEEEEE", 3);
t.rearrangeTasks("AAABC", 2);
t.rearrangeTasks("AAADBBCC", 2);
t.rearrangeTasks("AAADBBC", 2);
t.rearrangeTasks("CCCBBB", 2);
t.rearrangeTasks("CCCBBB", 3);
t.rearrangeTasks("AAAAAABBCCCCCDDDD", 2);
t.rearrangeTasks("AAAAAAAAAABBCCCCCDDDD", 2);
}
public int rearrangeTasks(String tasks, int cooldown){
HashMap<Character, Integer> occurMap = new HashMap<>();
//compute map
for (int i=0; i < tasks.length();i++) {
char c = tasks.charAt(i);
Integer occurence = occurMap.get(c);
if (occurence == null) {
occurMap.put(c, 1);
} else {
occurMap.put(c, occurence+1);
}
}
HashMap<Character, Integer> distMap = new HashMap<>();
final AtomicInteger startPos = new AtomicInteger(0);
AtomicInteger minDist = new AtomicInteger(tasks.length());
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
//placing same tasks far apart within minDist
int charDist = minDist.get() / occurence;
if (charDist <= cooldown) {
int newCharDist = (cooldown + 1);
distMap.put(c, newCharDist);
int newDist = (occurence-1) * newCharDist +
startPos.incrementAndGet();
if (minDist.get() < newDist) {
minDist.set(newDist);
}
} else {
distMap.put(c, charDist);
}
});
//only to print output task order, not required otherwse
AtomicInteger writePos = new AtomicInteger(-1);
char[] out = new char[minDist.get()];
Arrays.fill(out, '_');
occurMap.entrySet().stream().forEach( (e) -> {
char c = e.getKey();
int occurence = e.getValue();
int pos = writePos.incrementAndGet();
int charDist = distMap.get(c);
while(occurence > 0) {
while (out[pos] != '_' ||
anyInRange(out, pos-cooldown, pos+cooldown, c)) {
pos += (charDist + 1); //conflicts, moveover
pos %= minDist.get();
}
out[pos] = c;
occurence--;
pos += (charDist);
pos %= minDist.get();
}
});
System.out.println(new String(out) + " " + out.length);
return minDist.get();
}
private boolean anyInRange(char[] out, int i, int j, char c) {
if (i < 0) {
i = 0;
}
if (j >= out.length) {
j = out.length - 1;
}
for (int k = i; k <= j; k++) {
if (out[k] == c) {
return true;
}
}
return false;
}
}
Output:
ABC_ABC_ABC 11
ABCDEABCDEABCDEABCDEABCDE 25
ABCA__A 7
ABCADBAC 8
ABCABDA 7
BC_BC_BC 8
BC__BC__BC 10
ABCADCADCABCADCAD 17
ABCAD_AC_A_DA_CA_BAC_AD_ADCA 28
public int rearrange(List<Character> tasks, int k) {
if (tasks.size() == 1) return 1;
HashMap<Character, Integer> hm = new HashMap<>();
for (Character c: tasks) {
if (hm.contains(c)) hm.put(c, hm.get(c) + 1);
else (hm.add (c, 1));
}
// Sort tasks by frequency
ArrayList<Map.Entry> sortedTasks = Collections.sort(hm.entrySet().toArray(), (p1, p2) -> p1.value > p2.value);
// Add all tasks except the first, S
int sum = 0;
for (int i = 1; i < sortedTasks.size(); i++) {
sum += sortedTasks.get(i).value;
}
// If X is #of tasks of highest frequency, the formula for total duration is
// X + (X-1)k - S
return ((sortedTasks.get(0).value - 1) * k) - sum + sortedTasks.get(0).value;
}
My algorithm uses the following idea:
1. keep a HashMap of <Char, Int> as each char and its occurence in string.
2. Use a Deque to keep the current used window of K last inserted chars.
3. Build result picking the best available candidate as:
. has the max. number of count and was not recently inserted in the deque of K last chars.
. if none available pick an already existing element from deque starting from head and keep track of its cost of insertion to result.
Using a custom Tuple<Char, Int> class since Java 8 doesn't support Tuples out-of-the-box as to keep track of selected candidate <Char> and its cost to add to result <Int>.
Implementation in Java:
- guilhebl May 08, 2017