可以插入没有 3 个相邻字符的 X 的最大计数是 X

给定一个字符串，长度为N的str和一个字符X ，任务是找到要插入到字符串中的字符X的最大计数，使得没有三个连续字符等于X。如果找不到这样的字符串，则打印-1 。

例子：

Input: str = “xxyxy”, X = X 
Output: 3 
Explanation: 
Insert an ‘x’ at position 4: “xxyxxy”. 
Insert two ‘x’ at position 7: “xxyxxyxx” 
Now no more ‘x’ can be inserted, as it will lead to a size 3 substring with all x in it. 
Hence the required count is 3.

Input:str = “gfg”, X = ‘X’ 
Output: 8

方法：这个想法是计算可以插入X的所有位置，然后减去字符串中已经存在的X的计数。
以下是步骤：

1. 可以在字符串中插入的最大X数是2 * (N + 1) 个字符，因为可以在字符串的开头和结尾以及每个连续字符之间插入两个X。
2. 现在，找到大小为1或2的连续X组的数量，并将其存储在变量countX中。
3. 可以在给定字符串中插入的X数是2 *（要插入的位置数 + 1）- 找到的 X 数。
4. 总之，可以使用一个简单的数学公式2 * (N + 1) – (N – Xs)来找到最终答案。

下面是上述方法的实现：

C++14

// C++ program for the above approach
#include 
using namespace std;
 
// Utility function to find maximum count of
// X that are to be inserted into str such that
// no three consecutive characters are equal to X
int maxNumberOfXAddedUtil(string str, char X)
{
 
    // Stores count of consecutive X
    int countX = 0;
 
    // Stores count of characters which
    // is not equal to X
    int countNotX = 0;
 
    // Iterate over characters of string, str
    for (int i = 0; i < str.size(); i++)
    {
 
        // If current character is X
        if (str[i] == X)
        {
 
            // Update  countX
            countX++;
        }
 
        // If countX is less
        // than 3
        else if (countX < 3)
        {
 
            // Update countNotX
            countNotX++;
 
            // Update countX
            countX = 0;
        }
    }
 
    // If countX is greater than
    // or equal to 3
    if (countX >= 3)
        return -1;
    else
        return 2 * (countNotX + 1) - (str.size() - countNotX);
}
 
// Function to find maximum count of X that
// are to be inserted into str such that no
// three consecutive characters are equal to X
static void maxNumberOfXAdded(string str, char X)
{
 
    int ans = maxNumberOfXAddedUtil(str, X);
 
    // Print the answer
    cout << (ans);
}
 
// Driver code
int main()
{
 
    // Given string
    string str = "xxyxy";
 
    char X = 'x';
   
    // Function Call
    maxNumberOfXAdded(str, X);
}
 
// This code is contributed by amreshkumar3.

Java

// Java program for the above approach
 
import java.util.*;
 
public class Main {
 
    // Utility function to find maximum count of
    // X that are to be inserted into str such that
    // no three consecutive characters are equal to X
    static int maxNumberOfXAddedUtil(String str, char X)
    {
 
        // Stores count of consecutive X
        int countX = 0;
 
        // Stores count of characters which
        // is not equal to X
        int countNotX = 0;
 
        // Iterate over characters of string, str
        for (int i = 0; i < str.length(); i++) {
 
            // If current character is X
            if (str.charAt(i) == X) {
 
                // Update  countX
                countX++;
            }
 
            // If countX is less
            // than 3
            else if (countX < 3) {
 
                // Update countNotX
                countNotX++;
 
                // Update countX
                countX = 0;
            }
        }
 
        // If countX is greater than
        // or equal to 3
        if (countX >= 3)
            return -1;
        else
            return 2 * (countNotX + 1)
                - (str.length() - countNotX);
    }
 
    // Function to find maximum count of X that
    // are to be inserted into str such that no
    // three consecutive characters are equal to X
    static void maxNumberOfXAdded(String str, char X)
    {
 
        int ans = maxNumberOfXAddedUtil(str, X);
 
        // Print the answer
        System.out.println(ans);
    }
 
    // Driver Code
    public static void main(String[] args)
    {
 
        // Given string
        String str = "xxyxy";
 
        char X = X;
 
        // Function Call
        maxNumberOfXAdded(str, X);
    }
}

C#

// C# program for the above approach
using System;
 
class GFG{
 
    // Utility function to find maximum count of
    // X that are to be inserted into str such that
    // no three consecutive characters are equal to X
    static int maxNumberOfXAddedUtil(string str, char X)
    {
 
        // Stores count of consecutive X
        int countX = 0;
 
        // Stores count of characters which
        // is not equal to X
        int countNotX = 0;
 
        // Iterate over characters of string, str
        for (int i = 0; i < str.Length; i++) {
 
            // If current character is X
            if (str[i] == X) {
 
                // Update  countX
                countX++;
            }
 
            // If countX is less
            // than 3
            else if (countX < 3) {
 
                // Update countNotX
                countNotX++;
 
                // Update countX
                countX = 0;
            }
        }
 
        // If countX is greater than
        // or equal to 3
        if (countX >= 3)
            return -1;
        else
            return 2 * (countNotX + 1)
                - (str.Length - countNotX);
    }
 
    // Function to find maximum count of X that
    // are to be inserted into str such that no
    // three consecutive characters are equal to X
    static void maxNumberOfXAdded(string str, char X)
    {
 
        int ans = maxNumberOfXAddedUtil(str, X);
 
        // Print the answer
        Console.Write(ans);
    }
 
// Driver Code
public static void Main()
{
     // Given string
        string str = "xxyxy";
 
        char X = 'x';
 
        // Function Call
        maxNumberOfXAdded(str, X);
}
}
 
// This code is contributed by target_2.

Javascript

 
// JavaScript program for the above approach
 
// Utility function to find maximum count of
// X that are to be inserted into str such that
// no three consecutive characters are equal to X
function maxNumberOfXAddedUtil(str, X)
{
 
    // Stores count of consecutive X
    let countX = 0;
 
    // Stores count of characters which
    // is not equal to X
    let countNotX = 0;
 
    // Iterate over characters of string, str
    for (let i = 0; i < str.length; i++)
    {
 
        // If current character is X
        if (str[i] == X)
        {
 
            // Update countX
            countX++;
        }
 
        // If countX is less
        // than 3
        else if (countX < 3)
        {
 
            // Update countNotX
            countNotX++;
 
            // Update countX
            countX = 0;
        }
    }
 
    // If countX is greater than
    // or equal to 3
    if (countX >= 3)
        return -1;
    else
        return 2 * (countNotX + 1) - (str.length - countNotX);
}
 
// Function to find maximum count of X that
// are to be inserted into str such that no
// three consecutive characters are equal to X
function maxNumberOfXAdded(str,X)
{
 
    let ans = maxNumberOfXAddedUtil(str, X);
 
    // Print the answer
    document.write(ans);
}
 
// Driver code
 
// Given string
let str = "xxyxy";
 
let X = 'x';
 
// Function Call
maxNumberOfXAdded(str, X);
 
// This code is contributed by shinjanpatra
 

输出：

3

时间复杂度： O(N)
辅助空间： O(1)