比较复杂的模拟。

#include<iostream>
#include<vector>
using namespace std;
int N,M,gap;
vector<char> board;
void swap(int,int);
bool onboard(int);
int main()
{
    cin>>N>>M;
    board.resize(2*N+1+1);
    board[N+1]='S';gap=N+1;
    for (int i=1;i<=N;i++)  board[i]='W';
    for (int i=2+N;i<=2*N+1;i++)    board[i]='B';
    for (int i=1;i<=M;i++)
    {
        /*check if can jump*/
        /*check W jump*/
        if (onboard(gap-2)&&board[gap-2]=='W'&&board[gap-1]=='B'){
            swap(gap,gap-2);continue;
        }
        /*check B jump*/
        if (onboard(gap+2)&&board[gap+2]=='B'&&board[gap+1]=='W'){
            swap(gap,gap+2);continue;
        }
        /*check if can make same*/
        /*W*/ 
        if (onboard(gap-1)&&onboard(gap-2)&&
            board[gap-1]=='W'&&board[gap-2]=='W'){
                swap(gap,gap-1);continue;
            }
        /*B*/   
        if (onboard(gap+1)&&onboard(gap+2)&&
            board[gap+1]=='B'&&board[gap+2]=='B'){
                swap(gap,gap+1);continue;
            }
        /*else,just move one*/
        if (onboard(gap-1)&&board[gap-1]=='W')  swap(gap,gap-1);
        else                swap(gap,gap+1);
    }
    for (int i=1;i<=2*N+1;i++)  cout<<board[i];
return 0;
}

void swap(int g,int b)
{
    gap=b;
    board[g]=board[b];
    board[b]='S';
}

/*check is the position on board*/
bool onboard(int pos)
{
    return (pos>=1&&pos<=2*N+1);
}