[37] 解数独

/**
 * @param {character[][]} board
 * @return {void} Do not return anything, modify board in-place instead.
 */
var solveSudoku = function (board) {
  const canMatrix = new Array(9).fill([]).map(() => new Array(9).fill(false));
  let x = null;
  let y = null;
  for (let i = 8; i >= 0; i--) {
    for (let j = 8; j >= 0; j--) {
      if (board[i][j] === '.') {
        canMatrix[i][j] = true;
        board[i][j] = 0;
        x = i;
        y = j;
      } else {
        board[i][j] = Number(board[i][j]);
      }
    }
  }
  if (x === null) {
    return board;
  }
  // 判断是否冲突
  const hasConflict = function (i, j, val) {
    for (let e1 = 0; e1 < 9; e1++) {
      if ((e1 !== j && val === board[i][e1]) || (e1 !== i && val === board[e1][j])) {
        return false;
      }
    }
    const t1 = Math.floor(i / 3) * 3;
    const t2 = Math.floor(j / 3) * 3;
    for (let p1 = t1; p1 < t1 + 3; p1++) {
      for (let p2 = t2; p2 < t2 + 3; p2++) {
        if (val === board[p1][p2] && p1 !== i && p2 !== j) {
          return false;
        }
      }
    }
    return true;
  };
  // 获取下一个
  const getXY = function (x, y, direction) {
    if (direction) {
      if (y === 8) {
        x = x + 1;
        y = 0;
      } else {
        y = y + 1;
      }
    } else if (y === 0) {
      x = x - 1;
      y = 8;
    } else {
      y = y - 1;
    }
    return {
      x: x,
      y: y
    };
  };
  // 递归
  const fill = function (x, y, direction) {
    if (x > 8) {
      return;
    }
    if (canMatrix[x][y]) {
      let r = 0;
      for (let i = board[x][y] + 1; i <= 9; i++) {
        if (hasConflict(x, y, i)) {
          r = i;
          break;
        }
      }
      board[x][y] = r;
      if (r === 0) {
        const obj = getXY(x, y, false);
        fill(obj.x, obj.y, false);
      } else {
        const obj = getXY(x, y, true);
        fill(obj.x, obj.y, true);
      }
    } else {
      const obj = getXY(x, y, direction);
      fill(obj.x, obj.y, direction);
    }
  };
  fill(x, y, true);
  for (let i = 8; i >= 0; i--) {
    for (let j = 8; j >= 0; j--) {
      board[i][j] = String(board[i][j]);
    }
  }
  return board;
};