C++ - 任何人都可以帮助我将此for循环转换为递归function吗？

Question

I have an array, table, with some char, a and b. I want to find and replace the 'b' with 'a' then count how many are replaced. How to write a recursive function equivalent to the nested loop?

    const int length = 4;
    char table[length][length] = {
        {'a','b','a','a'},
        {'a','a','a','b'},
        {'a','a','b','a'},
        {'b','b','a','a'}
    };

    int count = 0;
    for (int i = 0; i < length; i++) {
        for (int j = 0; j < length; j++) {
            if (table[i][j] == 'b') {
                count++;
                table[i][j] = 'a';
            }
        }
    }
    cout << "Count: " << count << endl;

This is what I tried:

int replace_char(char array[][length], int row, int col) {
    // base cases and recursive
    if (row+1 != length - 1)
        replace_char(array, row+1, col);
    if (col+1 != length - 1)
        replace_char(array, row, col+1);

    // do this
    if (array[row][col] == 'b') {
        array[row][col] = 'a';
        return 1 + replace_char(array, row, col);
    }
    return 0;
}

My idea is, if it's not the end of the col or the row, then go check the next col or row. While checking, if the char is b, then return 1, and start checking from where it stops. But it is not working.

Answer 1

The function can be defined the following way as it is shown in the demonstrative program

#include <iostream>

size_t replace_count( char *s, size_t n, char c1 = 'b', char c2 = 'a' )
{
    return n == 0 ? 0 
                  : ( ( *s == c1 ? ( *s = c2, 1 ) : 0 ) + replace_count( s + 1, n - 1, c1, c2 ) );
}

int main() 
{
    const int length = 4;
    char table[length][length] = {
        {'a','b','a','a'},
        {'a','a','a','b'},
        {'a','a','b','a'},
        {'b','b','a','a'}
    };

    std::cout << replace_count( reinterpret_cast<char *>( table ), length * length )
              << '\n';

    return 0;
}

Its output is

5

Answer 2

Very close:

int replace_char(char array[][length], int row, int col) {
    if (col == length) {
        return replace_char(array, row + 1, 0); // reach the end of a col increment the
                                                // row by 1 and reset the col.
                                                // We are over the end so return
    }
    if (row == length) {
        // Then we have passed the last row simply return.
        return 0;
    }

    // Now do the work.
    int count = 0;
    if (array[row][col] == 'b') {
        array[row][col] = 'a';
        count = 1;
    }
    // Once you have done the work
    // Make the recursive call.
    return count + replace_char(array, row, col + 1);
}