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.
Approach #1: c++.
class Solution {
public:
string frequencySort(string s) {
unordered_map<char, int> mp;
string ans = "";
for (int i = 0; i < s.length(); ++i) {
mp[s[i]]++;
}
vector<pair<char, int>> v(mp.begin(), mp.end());
sort(v.begin(), v.end(), cmp);
for (int i = 0; i < v.size(); ++i) {
while (v[i].second--) {
ans += v[i].first;
}
}
return ans;
}
private:
static bool cmp(pair<char, int> a, pair<char, int> b) {
return a.second > b.second;
}
};