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Problem
Given a string, sort it in decreasing order based on the frequency of characters.
Example 1:
Input: "tree" Output: "eert"
Explanation:
"e" appears twice while "r" and "t" both appear once.
So "e" must appear before both "r" and "t". Therefore "eetr" is also a valid answer.
Example 2:
Input: "cccaaa" Output: "cccaaa"
Explanation:
Both "c" and "a" appear three times, so "aaaccc" is also a valid answer.
Note that "cacaca" is incorrect, as the same characters must be together.
Example 3:
Input: "Aabb" Output: "bbAa"
Explanation:
"bbaA" is also a valid answer, but "Aabb" is incorrect.
Note that "A" and "a" are treated as two different characters.
class Solution {
public String frequencySort(String s) {
Map map = new HashMap<>();
for (int i = 0; i < s.length(); i++) {
map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0)+1);
}
PriorityQueue> queue = new PriorityQueue<>((a, b)->b.getValue()-a.getValue());
queue.addAll(map.entrySet());
StringBuilder sb = new StringBuilder();
while (!queue.isEmpty()) {
Map.Entry entry = queue.poll();
for (int i = 0; i < (int)entry.getValue(); i++) sb.append(entry.getKey());
}
return sb.toString();
}
}
Bucket Sort
class Solution {
public String frequencySort(String s) {
Map map = new HashMap<>();
for (int i = 0; i < s.length(); i++) {
map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0)+1);
}
List[] buckets = new ArrayList[s.length()+1];
for (Map.Entry entry: map.entrySet()) {
int i = entry.getValue();
if (buckets[i] == null) buckets[i] = new ArrayList<>();
buckets[i].add(entry.getKey());
}
StringBuilder sb = new StringBuilder();
for (int i = s.length(); i >= 0; i--) {
if (buckets[i] != null && buckets[i].size() > 0) {
for (Character ch: buckets[i]) {
for (int j = i; j > 0; j--) sb.append(ch);
}
}
}
return sb.toString();
}
}
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