451. Sort Characters By Frequency
Đề Bài
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 1:
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.
Example 2:
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.
Example 3:
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 * 105sconsists of uppercase and lowercase English letters and digits.
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(n)
💾 Không gian
O(n)
Lời Giải
C++
0451-sort-characters-by-frequency.cpp
class Solution {
public:
unordered_map<int, int> um;
string frequencySort(string s) {
for (char c : s) {
um[c]++;
}
sort(s.begin(), s.end(), [&](char a, char b) {
if (um[a] != um[b]) {
return um[a] > um[b];
}
return a < b;
});
return s;
}
};