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.
思路：
Solution (C++):
string frequencySort(string s) {
if (s.empty()) return "";
int n = s.length();
vector<int> count(256, 0);
for (char c : s) ++count[c];
sort(s.begin(), s.end(), [&](char a, char b) {
return (count[a] > count[b]) || (count[a] == count[b] && a < b); });
return s;
}
性能：
Runtime: 104 ms Memory Usage: 8.2 MB
思路：
Solution (C++):
性能：
Runtime: ms Memory Usage: MB
