如何统计字符串‘rajarajeshwari’中字母‘a’的出现次数

Python 实现 #

最直接的方法是用字符串内置的count()方法：

s = 'rajarajeshwari'
a_count = s.count('a')
print(a_count)  # 输出: 5

如果需要手动遍历理解逻辑：

s = 'rajarajeshwari'
count = 0
for char in s:
    if char == 'a':
        count += 1
print(count)  # 输出: 5

JavaScript 实现 #

通过split()拆分后计算长度差：

const s = 'rajarajeshwari';
const aCount = s.split('a').length - 1;
console.log(aCount); // 输出: 5

手动遍历版本：

const s = 'rajarajeshwari';
let count = 0;
for (let char of s) {
    if (char === 'a') count++;
}
console.log(count); // 输出: 5

Java 实现 #

循环遍历字符数组：

public class CountChar {
    public static void main(String[] args) {
        String s = "rajarajeshwari";
        int count = 0;
        for (char c : s.toCharArray()) {
            if (c == 'a') {
                count++;
            }
        }
        System.out.println(count); // 输出: 5
    }
}

或者用Stream API简化：

import java.util.stream.IntStream;

public class CountChar {
    public static void main(String[] args) {
        String s = "rajarajeshwari";
        long count = s.chars().filter(c -> c == 'a').count();
        System.out.println(count); // 输出: 5
    }
}

内容的提问来源于stack exchange，提问作者Balaji Viswanathan