java - 使用 java 的 for 循环计算给定字符串中某个字符的出现次数

Question

这是引用代码:

    // Create an array of size 256 i.e. ASCII_SIZE
    int count[] = new int[MAX_CHAR];

    int len = str.length();

    // Initialize count array index
    for (int i = 0; i < len; i++)
        count[str.charAt(i)]++;

    // Create an array of given String size
    char ch[] = new char[str.length()];
    for (int i = 0; i < len; i++) {
        ch[i] = str.charAt(i);
        int find = 0;
        for (int j = 0; j <= i; j++) {

            // If any matches found
            if (str.charAt(i) == ch[j])
                find++;
        }

        if (find == 1)
            System.out.println("Number of Occurrence of " +
                    str.charAt(i) + " is:" + count[str.charAt(i)]);
    }

输出应该类似于:

Number of occurrence of 'x' is: 'times it occured'

如果该字母之前出现过，则仅显示该字母一次。

<小时/>

我使用 2 个 for 循环得到逻辑，尽管我的老师说只使用 1 个 for 循环就可以执行这个应用程序。

我遇到的问题是:
仅当角色彼此相邻时，我才能确定该角色是否已被找到。

您如何在没有另一个 for 循环的情况下检查是否已找到所有先前的字符？

Answer 1

使用 Map<Integer, Integer> (键:字符，值:字符数)来存储您的字符数。

你只需要循环你的角色一次:

String input = "this is input string";
Map<Integer, Integer> charCount = new LinkedHashMap<>();
for (int c : input.toCharArray()) {
    if (!charCount.containsKey(c)) {
       charCount.put(c, 1);
    } else {
       charCount.put(c, charCount.get(c) + 1);
    }
}

// Here you print the char count:
for (Entry<Integer, Integer> entry : charCount.entrySet()) {
    // (char) entry.getKey() is the character
    // entry.getValue() is number of occurence
}

没有Map :

int[][] count = new int[MAX_CHAR][2];
for (int c : input.toCharArray()) {
    count[c][0] += 1; // Increase occurrence by 1
    count[c][1] = 1; // Mark this character exists in string
}
// Here you can print the count of char per character
// Not that, you can use count[c][1] to determine that if the character exists in your String
for (int i = 0; i < MAX_CHAR; i++) {
    if (count[i][1] == 1) {
        System.out.println("Char: " + (char) i + " Occurence: " + count[i][0]);
    }
}

编辑正如 @oreh 所建议的，我们甚至不需要二维数组:

int[] count = new int[MAX_CHAR];
for (int c : input.toCharArray()) {
    count[c][0] += 1; // Increase occurrence by 1
}
for (int i = 0; i < MAX_CHAR; i++) {
    if (count[i] > 0) {
        System.out.println("Char: " + (char) i + " Occurence: " + count[i]);
    }
}