算法思路

解析FEN字符串：将FEN字符串转换为一个8x8的棋盘表示。

标记被攻击的方格：对于棋盘上的每一个棋子，根据其类型和位置，标记所有它能攻击的方格。

统计安全空格：统计那些既没有被任何棋子占据，也没有被任何棋子攻击的方格数量。

算法代码

#include <iostream>
#include <vector>
#include <string>
#include <cctype>

using namespace std;

const int BOARD_SIZE = 8;

// 检查坐标是否在棋盘内
bool isOnBoard(int x, int y) {
    return x >= 0 && x < BOARD_SIZE && y >= 0 && y < BOARD_SIZE;
}

// 标记被攻击的格子
void markAttacked(vector<vector<bool>>& attacked, int x, int y, int dx, int dy, const vector<vector<char>>& board) {
    x += dx;
    y += dy;
    while (isOnBoard(x, y)) {
        attacked[x][y] = true;
        if (board[x][y] != ' ') break;
        x += dx;
        y += dy;
    }
}

// 处理每个棋子的攻击范围
void processPiece(vector<vector<bool>>& attacked, int x, int y, char piece, const vector<vector<char>>& board) {
    switch (tolower(piece)) {
        case 'p': {
            int dir = isupper(piece) ? -1 : 1;
            if (isOnBoard(x + dir, y - 1)) attacked[x + dir][y - 1] = true;
            if (isOnBoard(x + dir, y + 1)) attacked[x + dir][y + 1] = true;
            break;
        }
        case 'n': {
            int knightMoves[8][2] = {{-2, -1}, {-2, 1}, {-1, -2}, {-1, 2}, {1, -2}, {1, 2}, {2, -1}, {2, 1}};
            for (int i = 0; i < 8; ++i) {
                int newX = x + knightMoves[i][0];
                int newY = y + knightMoves[i][1];
                if (isOnBoard(newX, newY)) attacked[newX][newY] = true;
            }
            break;
        }
        case 'b': {
            markAttacked(attacked, x, y, -1, -1, board);
            markAttacked(attacked, x, y, -1, 1, board);
            markAttacked(attacked, x, y, 1, -1, board);
            markAttacked(attacked, x, y, 1, 1, board);
            break;
        }
        case 'r': {
            markAttacked(attacked, x, y, -1, 0, board);
            markAttacked(attacked, x, y, 1, 0, board);
            markAttacked(attacked, x, y, 0, -1, board);
            markAttacked(attacked, x, y, 0, 1, board);
            break;
        }
        case 'q': {
            markAttacked(attacked, x, y, -1, -1, board);
            markAttacked(attacked, x, y, -1, 1, board);
            markAttacked(attacked, x, y, 1, -1, board);
            markAttacked(attacked, x, y, 1, 1, board);
            markAttacked(attacked, x, y, -1, 0, board);
            markAttacked(attacked, x, y, 1, 0, board);
            markAttacked(attacked, x, y, 0, -1, board);
            markAttacked(attacked, x, y, 0, 1, board);
            break;
        }
        case 'k': {
            int kingMoves[8][2] = {{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1}};
            for (int i = 0; i < 8; ++i) {
                int newX = x + kingMoves[i][0];
                int newY = y + kingMoves[i][1];
                if (isOnBoard(newX, newY)) attacked[newX][newY] = true;
            }
            break;
        }
    }
}

// 根据 FEN 字符串构建棋盘
vector<vector<char>> buildBoard(const string& fen) {
    vector<vector<char>> board(BOARD_SIZE, vector<char>(BOARD_SIZE, ' '));
    int x = 0, y = 0;
    for (char c : fen) {
        if (c == '/') {
            x++;
            y = 0;
        } else if (isdigit(c)) {
            y += c - '0';
        } else {
            board[x][y] = c;
            y++;
        }
    }
    return board;
}

// 计算未被攻击的空格数
int countUnattacked(const vector<vector<char>>& board) {
    vector<vector<bool>> attacked(BOARD_SIZE, vector<bool>(BOARD_SIZE, false));
    for (int i = 0; i < BOARD_SIZE; ++i) {
        for (int j = 0; j < BOARD_SIZE; ++j) {
            if (board[i][j] != ' ') {
                processPiece(attacked, i, j, board[i][j], board);
            }
        }
    }
    int count = 0;
    for (int i = 0; i < BOARD_SIZE; ++i) {
        for (int j = 0; j < BOARD_SIZE; ++j) {
            if (board[i][j] == ' ' && !attacked[i][j]) {
                count++;
            }
        }
    }
    return count;
}

int main() {
    string fen;
    while (cin >> fen) {
        vector<vector<char>> board = buildBoard(fen);
        int result = countUnattacked(board);
        cout << result << endl;
    }
    return 0;
}