// T1313 位数问题

#include <iostream>
using namespace std;

const int MAXN = 25;

bool vis[MAXN][MAXN]; // 默认初始化为 0，代表可以走
long long arr[MAXN][MAXN]; 

int main() {
    int n, m; // 横盘的大小
    int x, y; // 马所在的坐标
    
    cin >> n >> m >> x >> y;
    
    vis[x][y] = true; // 马所在位置是不能走的
    // 8 个控制点也不能走
    const int controls[8][2] = {
      {2, 1}, // P1
      {1, 2}, // P2
      {-1, 2}, // P3
      {-2, 1}, // P4
      {-2, -1}, // P5
      {-1, -2}, // P6
      {1, -2}, // P7
      {2, -1} // P8
    };
    
    for (int i = 0; i < 8; i++) {
      int nx = x + controls[i][0];
      int ny = y + controls[i][1];
      
      if (nx >= 0 && nx <= n && ny >= 0 && ny <= m) {
        vis[nx][ny] = true; // 计算出的控制点不能走
      }
    }
    
    for (int i = 0; i <= n; i ++) {
      for (int j = 0; j <= m; j++) {
        if (true == vis[i][j]) {
          arr[i][j] = 0; // 走到马或控制点所在位置，将路径数清零
        } else if (i == 0 || j == 0) {
          arr[i][j] = 1;
        } else {
          // 每个点所在位置的走法只能来自左边一个点或上边一个点
          arr[i][j] = arr[i - 1][j] + arr[i][j - 1];
        }
      }
    }
    
    cout << arr[n][m] << endl;
    
    return 0;
}
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About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}