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//  undefined

包装类执行完就销毁了

function numRookCaptures(board){  let xR = -1,      yR = -1,      count = 0;  for(let i = 0; i < 8; i++){    if(board[i].indexOf('R') != -1 ){      xR = i;      yR = board[i].indexOf('R');      break;    }  }  // up  for(let i = xR; i >= 0; i--){    if(board[i][yR] == 'p' || board[i][yR] == 'B') {      if(board[i][yR] == 'p'){        count++;      }      break;    }  }  // down  for(let i = xR; i < 8; i++){    if(board[i][yR] === 'p' || board[i][yR] == 'B'){      if(board[i][yR] == 'p'){        count++;      }      break;    }  }  // left  for(let j = yR; j >= 0; j--){    if(board[xR][j] == 'p' || board[xR][j] == 'B'){      if(board[xR][j] == 'p'){        count++;      }      break;    }  }  // right  for(let j = yR; j < 8; j++){    if(board[xR][j] == 'p' || board[xR][j] === 'B'){      if(board[xR][j] == 'p'){        count++;      }      break;    }  }  return count;}let arr0 = [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","R",".",".",".","p"],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]let arr1 = [[".",".",".",".",".",".",".","."],[".","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",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]let arr2 = [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","p",".",".",".","."],["p","p",".","R",".","p","B","."],[".",".",".",".",".",".",".","."],[".",".",".","B",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".",".",".",".",".","."]]let arr3 = [[".",".",".",".",".",".",".","."],[".",".",".","p",".",".",".","."],[".",".",".","R",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]let arr5 = [[".",".",".",".",".",".",".","."],[".",".","B","B","B","B","B","."],[".",".","B",".",".",".","B","."],[".",".","B",".","R",".","B","."],[".",".","B",".",".",".","B","."],[".",".","B","B","B","B","B","."],[".",".",".",".",".",".",".","."],[".",".",".",".",".",".",".","."]]

方向数组方法更也不错

var numRookCaptures = function(board) {    let cnt = 0, st = 0, ed = 0;    const dx = [0, 1, 0, -1];    const dy = [1, 0, -1, 0];    for (let i = 0; i < 8; ++i) {        for (let j = 0; j < 8; ++j) {            if (board[i][j] == 'R') {                st = i;                ed = j;                break;            }        }    }    for (let i = 0; i < 4; ++i) {        for (let step = 0;; ++step) {            const tx = st + step * dx[i];            const ty = ed + step * dy[i];            if (tx < 0 || tx >= 8 || ty < 0 || ty >= 8 || board[tx][ty] == 'B') {                break;            }            if (board[tx][ty] == 'p') {                cnt++;                break;            }        }    }    return cnt;};

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