Given a string s, sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string.
Return the sorted string. If there are multiple answers, return any of them.
Example:
Input: s = "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.
Input: s = "cccaaa"
Output: "aaaccc"
Explanation: Both 'c' and 'a' appear three times, so both "cccaaa" and "aaaccc" are valid answers.
Note that "cacaca" is incorrect, as the same characters must be together.
Input: s = "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.
Constraints:
- 1 <= s.length <= 5 * 105
- s consists of uppercase and lowercase English letters and digits.
計算字串內個別字元的個數大小，再排序後回傳
public class Solution {
public string FrequencySort(string s) {
if (s == null || s.Length <= 1)
{
return s;
}
var map = new Dictionary<char, int>();
var cs = s.ToCharArray();
//把裡面的值塞進Dictionary裡面統計
for (int i = 0; i < cs.Length; i++)
{
if (map.ContainsKey(cs[i]))
{
map[cs[i]]++;
} else
{
map.Add(cs[i], 1);
}
}
//先依照出現次數排序
var sort = map.OrderByDescending(x => x.Value);
var result = new StringBuilder();
//還原字串
foreach (var item in sort)
{
for (int i = 0;i <item.Value;i++)
{
result.Append(item.Key);
}
}
return result.ToString();
}
}