Question

我需要确定一个递归函数crosssum :: Int - ＆gt;在Haskell中Int来计算正数的交叉和。除了（:)，（＆gt;），（++），（＆lt;），（＆gt; =），（＆lt; =），div，mod，not之外，我不允许使用分层库中的任何函数。＆amp;＆amp;），max，min等。

crosssum :: Int -> Int 
cross sum x = if x > 0 
          then x `mod` 10 
          + x `div` 10 + crosssum x 
          else 0

所以每当我填写例如crosssum 12它说'线程被杀'。我不明白如何做到这一点。我很感激任何想法。谢谢

Answer 1

您的代码存在的一个问题是x在crosssum的递归调用作为参数传递时不会减少（或以某种方式更改）。这就是为什么你的程序永远不会停止的原因。

修改后的代码：

crosssum :: Int -> Int
crosssum x = if x > 0
             then x `mod` 10 + crosssum (x `div` 10)
             else 0

将具有以下逻辑

crosssum 12 = 2 + (crosssum 1) = 2 + (1 + (crosssum 0)) = 2 + 1 + 0

顺便说一句，Haskell将通过使用模式匹配来帮助您避免if条件，以获得更易读的代码：

crosssum :: Int -> Int
crosssum 0 = 0
crosssum x =
  (mod x 10) + (crosssum (div x 10))

Answer 2

Prelude中的divMod也非常方便。这是

var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
var view = {x: 0, y: 0};
var questionsArray = [];
var moveCount = 0;
var mapArray = [
  [0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 2, 2, 0],
  [0, 0, 1, 1, 1, 0, 0, 2, 0, 0],
  [0, 0, 1, 1, 1, 0, 0, 0, 0, 0],
  [0, 0, 0, 1, 1, 1, 1, 1, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 1, 1, 0, 0, 0, 0],
  [0, 0, 0, 0, 1, 1, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 2, 2, 0],
  [0, 0, 1, 1, 1, 0, 0, 2, 0, 0],
  [0, 0, 1, 1, 1, 0, 0, 0, 0, 0],
  [0, 0, 0, 1, 1, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 1, 1, 0, 0, 0, 0],
  [0, 0, 0, 0, 1, 1, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
];

function isPositionWall(ptX, ptY) {
  var gridX = Math.floor(ptX / 36)
  var gridY = Math.floor(ptY / 36)
  if(gridX < 0 || gridX >= mapArray[0].length)
    return true;
  if(gridY < 0 || gridY >= mapArray.length)
    return true;
    return mapArray[gridX][gridY];
}
var theArray = [];
var Question = function(question, answer1, answer2, correctAnswer) {
  this.question = question;
  this.answer1 = answer1;
  this.answer2 = answer2;
  this.correctAnswer = correctAnswer;

  this.addToArray = function(){
     theArray.push(this);
 };
  this.addToArray();
}

Question.prototype.checkAnswer = function() {
  return answer1 || answer2 == correctAnswer;
}

var question1 = new Question("Taip ar ne?", "Taip", "Ne", "Taip");
var question2 = new Question("Jo ar ne?", "Ne", "Jo", "Jo");
var question3 = new Question("Aha ar ne?", "Aha", "Ne", "Ne");
var question4 = new Question("Ja ar ne?", "Taip", "Ne", "Taip");
var question5 = new Question("Jojo ar ne?", "Taip", "Ne", "Taip");
var question6 = new Question("Taip ar ne?", "Taip", "Ne", "Taip");
var question7 = new Question("Taip ar ne?", "Taip", "Ne", "Taip");


var StyleSheet = function(image, width, height, x, y) {
  this.image = image;
  this.width = width;
  this.height = height;
  this.x = x;
  this.y = y
  this.draw = function(image, sx, sy, swidth, sheight, x, y, width, height) {
    context.drawImage(image, sx, sy, swidth, sheight, x, y, width, height);
  };
  this.drawimage = function(image, x, y, width, height) {
    context.drawImage(image, x, y, width, height);
  };
};

/* Initial Sprite Position */


var boatPosX = canvas.height/2 - 50;
var boatPosY = canvas.height/2 - 50;

function render(viewport) {
  context.save();
  context.translate(view.x, view.y);
  requestAnimationFrame(render);
  var oldPosX = boatPosX;
  var oldPosY = boatPosY;
  for (let i = 0; i < mapArray.length; i++) {
    for (let j = 0; j < mapArray[i].length; j++) {
      if (mapArray[i][j] == 0) {
        this.sprite.draw(
          background,
          190,
          230,
          26,
          26,
          i * this.sprite.width,
          j * this.sprite.height,
          this.sprite.width,
          this.sprite.height
        );
      }
      if (mapArray[i][j] == 1) {
        this.sprite.draw(
          background,
          30,
          30,
          26,
          26,
          i * this.sprite.width,
          j * this.sprite.height,
          this.sprite.width,
          this.sprite.height
        );

      }
      if (mapArray[i][j] == 2) {
        this.sprite.draw(
          background,
          200,
          20,
          26,
          26,
          i * this.sprite.width,
          j * this.sprite.height,
          this.sprite.width,
          this.sprite.height
        );
      }
    }
  }
  this.ship.drawimage(boat, boatPosX, boatPosY, 50, 50);
  //console.log(boatPosX + ship.width)
  if(isPositionWall(boatPosX, boatPosY)) {
    boatPosX = oldPosY;
    console.log("collision");
  }

  context.restore();

};

function move(e) {
  if (e.keyCode == 39) {
    boatPosX += 5;
    //canvas.width += 2;
    view.x -= 5
    moveCount++;
    console.log(moveCount);
    console.log("right");
    context.fillStyle = "red";
    context.fillText(theArray[0].question, 0, 0);
    console.log(theArray[0].question);
  }
  if (e.keyCode == 37) {
    boatPosX -= 5;
    view.x += 5
    moveCount++;
    console.log(moveCount);
    console.log("left");
  }
  if (e.keyCode == 38) {
    boatPosY -= 5;
    view.Y += 5
    moveCount++;
    console.log(moveCount);
    console.log("up");
  }
  if (e.keyCode == 40) {
    boatPosY += 5;
    view.Y += 5
    moveCount++;
    console.log(moveCount);
    console.log("down");
  }
}

document.onkeydown = move;

var background = new Image();
background.src = "ground.png";
var sprite = new StyleSheet(background, 36, 36, 16, 16);

var boat = new Image();
boat.src = "ship.png";
var ship = new StyleSheet(boat, 90, 100, 16, 16);
console.log(Math.floor(boatPosX / 36));
console.log(mapArray[Math.floor(boatPosX / 36)]);


render();

和div的一项操作，事实上对于所有2位数字mod

dm n = sum.sequence [fst,snd] $ divMod n 10

cs将执行任何大小编号。

Haskell中的交叉和运算

2 个答案: