【LeetCode】999. Available Captures for Rook 解题报告(C++)

• 作者： 负雪明烛
• id： fuxuemingzhu
• 个人博客：http://fuxuemingzhu.cn/

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目录

• • 题目描述
  • 题目大意
  • 解题方法
  • • 四方向搜索
  • 日期

题目地址：https://leetcode.com/problems/available-captures-for-rook/

题目描述

On an 8 x 8 chessboard, there is one white rook. There also may be empty squares, white bishops, and black pawns. These are given as characters 'R', '.', 'B', and 'p' respectively. Uppercase characters represent white pieces, and lowercase characters represent black pieces.

The rook moves as in the rules of Chess: it chooses one of four cardinal directions (north, east, west, and south), then moves in that direction until it chooses to stop, reaches the edge of the board, or captures an opposite colored pawn by moving to the same square it occupies. Also, rooks cannot move into the same square as other friendly bishops.

Return the number of pawns the rook can capture in one move.

Example 1:

Input: [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","R",".",".",".","p"],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]
Output: 3
Explanation: 
In this example the rook is able to capture all the pawns.

Example 2:

Input: [[".",".",".",".",".",".",".","."],[".","p","p","p","p","p",".","."],[".","p","p","B","p","p",".","."],[".","p","B","R","B","p",".","."],[".","p","p","B","p","p",".","."],[".","p","p","p","p","p",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]
Output: 0
Explanation: 
Bishops are blocking the rook to capture any pawn.

Example 3:

Input: [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","p",".",".",".","."],["p","p",".","R",".","p","B","."],[".",".",".",".",".",".",".","."],[".",".",".","B",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."]]
Output: 3
Explanation: 
The rook can capture the pawns at positions b5, d6 and f5.

Note:

1. board.length == board[i].length == 8
2. board[i][j] is either 'R', '.', 'B', or 'p'
3. There is exactly one cell with board[i][j] == 'R'

题目大意

国际象棋的棋盘上有一个白方的车，还有若干个白方的象，还有若干黑方的卒。车可以向四个方向行走，白色的象会挡住车的去路，问最多能吃掉多少个黑色的卒。

解题方法

四方向搜索

这个题和炸弹人的题目是一样的。

1. 先找到白色的车的位置；
2. 然后从该位置出发，向四个方向进行搜索，如果遇到边界或者白色的象那么停止搜索；遇到黑色的卒那么就把能吃的卒的数目加1，并且也要停止搜索。

C++代码如下：

class Solution {
public:
    int numRookCaptures(vector<vector<char>>& board) {
        int N = 8;
        int row = -1;
        int col = -1;
        bool findR = false;
        for (int i = 0; i < N && !findR; ++i) {
            for (int j = 0; j < N && !findR; ++j) {
                if (board[i][j] == 'R') {
                    row = i;
                    col = j;
                    break;
                }
            }
        }
        int res = 0;
        for (auto& dir : directions) {
            int x = row;
            int y = col;
            while (true) {
                x += dir[0];
                y += dir[1];
                if (x < 0 || x >= N || y < 0 || y >= N 
                    || board[x][y] == 'B') {
                    break;
                }
                if (board[x][y] == 'p') {
                    res ++;
                    break;
                }
            }
        }
        return res;
    }
    vector<vector<int>> directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
};

日期

2020 年 3 月 26 日 —— 江南烟雨