Java使用字符和数字生成字符串的不同方式

给定一个数字num和 String str ，任务是通过使用数字的索引值从字符串提取字符来生成新的 String 。

例子：

Input: str = “GeeksforGeeks”

           num = 858

Output: GfG

Explanation: The 8th, 5th, and 8th position of the characters are extracting from the given string and generate a new string.

Input: str = “Java”

           num = 12

Output: The 1st and 2nd position of the characters are extracting from the given string and generate a new string.
 

方法 1：使用两次遍历

1. 获取字符串和数字以生成新字符串。
2. 初始化一个存储最终答案的变量。
3. 将给定的数字转换为字符串。
4. 从头到尾遍历循环。
5. 获取数字的最后一位并将第 k 个位置字符添加到变量 answer 中。
6. 以相反的顺序遍历循环并将第j 个位置字符添加到变量finalAnswer 中。
7. 现在，打印结果。

Java

// Java program to generate String by using
// Strings and numbers
class GFG {
  
    // Function to generate the new String
    public static String generateNewString(String str,
                                           int num)
    {
        // Initialize a variable that
        // stores the final anser.
        String finalAnswer = "";
  
        String answer = "";
  
        // Converting the given numbers
        // into string
        String index = String.valueOf(num);
  
        // Traverse the loop from start to end
        for (int i = 0; i < index.length(); i++) {
  
            // Getting last digit of numbers
            int k = num % 10;
  
            // Adding kth position character
            // into the variable answer
            answer = answer + str.charAt(k);
            num = num / 10;
        }
  
        // Traverse the loop in reverse order
        for (int j = answer.length() - 1; j >= 0; j--) {
  
            // Adding jth position character
            // into the variable finalAnswer
            finalAnswer = finalAnswer + answer.charAt(j);
        }
  
        // Return the finalAnswer
        return finalAnswer;
    }
  
    // Driver Code
    public static void main(String args[])
    {
  
        // Given String str
        String str = "GeeksforGeeks";
  
        // Given Number num
        int num = 858;
  
        // Printing the result
        System.out.println(generateNewString(str, num));
    }
}

输出

GfG

方法 2：使用一次遍历

1. 获取字符串和数字以生成新字符串。
2. 初始化一个存储结果的变量。
3. 将给定的数字转换为字符串。
4. 从头到尾遍历循环。
5. 获取正确的索引并将第 k 个位置字符添加到结果中。
6. 现在，打印结果。

Java

// Java program to generate String by using
// Strings and numbers
class GFG {
  
    // Function to generate the new String
    public static String generateNewString(String str,
                                           int num)
    {
        // Initialize a variable that
        // stores the result.
        String result = "";
  
        // Converting the given numbers
        // into the string
        String index = String.valueOf(num);
  
        // Traverse the loop from start to end
        for (int i = 0; i < index.length(); i++) {
  
            // Getting the right index
            int k = index.charAt(i) - 48;
  
            // Adding kth position character
            // into the result
            result = result + str.charAt(k);
        }
  
        // Return result
        return result;
    }
  
    // Driver Code
    public static void main(String args[])
    {
  
        // Given String str
        String str = "GeeksforGeeks";
  
        // Given Number num
        int num = 858;
  
        // Printing the result
        System.out.println(generateNewString(str, num));
    }
}

输出

GfG

时间复杂度： O(N)

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