题解 | 统计字符

#include <iostream>
#include <unordered_map>
using namespace std;

class Solution {
public:
    char firstCharThreeTimes(const string& str) {
        unordered_map<char, int> charCount;
        
        for (char c : str) {
            if (isalpha(c)) {  // 只考虑字母
                charCount[c]++;
                if (charCount[c] == 3) {
                    return c;
                }
            }
        }
        
        return '\0'; // 如果没有字符出现三次，返回空字符
    }
};

int main() {
    string input;
    getline(cin, input);
    
    Solution solution;
    char result = solution.firstCharThreeTimes(input);
    
    if (result != '\0') {
        cout << result << endl;
    } else {
        cout << "No character appears three times." << endl;
    }
    
    return 0;
}

import java.util.*;

public class Main {
    public static char firstCharThreeTimes(String str) {
        Map<Character, Integer> charCount = new HashMap<>();
        
        for (char c : str.toCharArray()) {
            if (Character.isLetter(c)) {  // 只考虑字母
                charCount.put(c, charCount.getOrDefault(c, 0) + 1);
                if (charCount.get(c) == 3) {
                    return c;
                }
            }
        }
        
        return '\0'; // 如果没有字符出现三次，返回空字符
    }
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String input = sc.nextLine();
        
        char result = firstCharThreeTimes(input);
        
        if (result != '\0') {
            System.out.println(result);
        } else {
            System.out.println("No character appears three times.");
        }
    }
}

class Solution:
    def firstCharThreeTimes(self, s):
        char_count = {}
        
        for c in s:
            if c.isalpha():  # 只考虑字母
                char_count[c] = char_count.get(c, 0) + 1
                if char_count[c] == 3:
                    return c
        
        return None  # 如果没有字符出现三次，返回None

if __name__ == "__main__":
    input_str = input().strip()
    
    solution = Solution()
    result = solution.firstCharThreeTimes(input_str)
    
    if result is not None:
        print(result)
    else:
        print("No character appears three times.")