body {
  font-family: cursive;
  font-size: 14pt;
  text-align: center;
}

#puzzlearea {
  height: 400px;
  margin: 0 auto;
  position: relative;
  width: 400px;
}

.highlight {
  border-color: red;
  cursor: pointer;
}

.puzzletile {
  background-image: url("../background.jpg");
  border: 5px solid black;
  position: absolute;
}

.highlight, #output {
  color: red;
}

.puzzletile, #output {
  font-size: 40pt;
}

  
  
  
  
  



Fifteen Puzzle


  The goal of the fifteen puzzle is to un-jumble its fifteen squares
  by repeatedly making moves that slide squares into the empty space.
  How quickly can you solve it?



  



  Shuffle





  American puzzle author and mathematician Sam Loyd is often falsely
  credited with creating the puzzle; indeed, Loyd claimed from 1891
  until his death in 1911 that he invented it.
  The puzzle was actually created around 1874 by Noyes Palmer Chapman,
  a postmaster in Canastota, New York.

(function () {
  "use strict";

  let NUM = 4; //拼图的行列数 the number of rows/cols in the puzzle
  let spaceRow = 3; // 空白图块所在行
  let spaceColumn = 3; // 空白图块所在列
  let WIDTH = 100; // the pixel width/height of each tile

  // gets everything set when the window has loaded
  window.onload = function () {
   setSize();
   document.getElementById("select").onchange = changeSize;
   document.getElementById("shufflebutton").onclick = shuffle;
   createSquares();

  };

  // add a drop-down list to select difficulty level
  // 设置下拉列表 默认选中 option4
  function setSize() {
   var select = document.createElement("select");
   select.id = "select";
   for (var i = 3; i < 7; i++) {
     var option = document.createElement("option");
     option.innerHTML = i + " * " + i;
     option.value = i;
     option.id = "option" + i;
     select.appendChild(option);
   }
   document.getElementById("controls").appendChild(select);
   document.getElementById("option4").selected = "selected";
  }


  function changeSize() {
   NUM = this.value;
   spaceRow = this.value - 1;
   spaceColumn = this.value - 1;
   WIDTH = parseInt(400 / this.value);
   var puzzlearea = document.getElementById("puzzlearea");
   while (puzzlearea.contains(document.querySelector(".puzzletile"))) {
     puzzlearea.removeChild(document.querySelector(".puzzletile"));
   }
   createSquares();
  }

  // creates 15 puzzle tiles and sets them to their initial position
  function createSquares() {
   for (var i = 1; i < NUM * NUM; i++) {
     var div = document.createElement("div");
     div.className = "puzzletile";
     div.innerHTML = i;
     var row = Math.floor((i - 1) / NUM);
     var column = (i - 1) % NUM;
     var x = column * -1 * WIDTH + "px";
     var y = row * -1 * WIDTH + "px";

     // 减去边框的宽度 并且宽高相等
     div.style.height = WIDTH - 10 + "px";
     div.style.width = div.style.height;
     // 设置background 的 position
     div.style.backgroundPosition = x + " " + y;
     // 为每个拼图添加ID
     div.id = "square_" + row + "_" + column;
     // 设置水平和垂直方向的偏移量
     div.style.top = row * WIDTH + "px";
     div.style.left = column * WIDTH + "px";
     setEvents(div);
     document.getElementById("puzzlearea").appendChild(div);
   }
  }

  // shuffles puzzle tiles for 1000 times
  function shuffle() {
   // 实现Shuffle算法
   for (let j = 0; j < 1000; j++) {
     let neigbors = [];
     // 将所有的拼图 存储到 allPuzzles中
     let allPuzzles = document.getElementsByClassName("puzzletile");
     // 将与空白图块相邻的拼图 存储到数组neigbors中
     for (let i = 0; i < allPuzzles.length; i++) {
      // 判断拼图是否可以移动
      if (moveable(allPuzzles[i]))
        neigbors.push(allPuzzles[i]);
      }
     // 得到一个随机的索引
     let ranNum = getRandomIntInclusive(0, neigbors.length - 1);
     // 获取需要移动的拼图移动之前的偏移量
     let tempTop = neigbors[ranNum].style.top;
     let tempLeft = neigbors[ranNum].style.left;
     // 将拼图移动到空白图块处
     neigbors[ranNum].style.top = spaceRow * WIDTH + "px";
     neigbors[ranNum].style.left = spaceColumn * WIDTH + "px";
     neigbors[ranNum].id = "square_" + spaceRow + "_" + spaceColumn;
     // 更改空白图块的位置
     spaceRow = parseInt(tempTop) / WIDTH;
     spaceColumn = parseInt(tempLeft) / WIDTH;
   }


  }

  // 获取指定区间的随机数
  function getRandomIntInclusive(min, max) {
   min = Math.ceil(min);
   max = Math.floor(max);
   return Math.floor(Math.random() * (max - min + 1)) + min;
  }

  // sets up events for all puzzle tiles
  function setEvents(div) {
   div.onmouseover = function () {
     if (moveable(this)) {
      this.classList.add("highlight"); // when mouse over, adds class "highlight"
     }
   };
   div.onmouseout = function () {
     // when mouse out, removes class "highlight"
     if (moveable(this)) {
      this.classList.remove("highlight"); // when mouse out, remove class "highlight"
     }
   };
   div.onclick = helper;
  }

  // a helper function for function "makeAMove"
  // displays "congratulations" if the player wins
  function helper() {
   if (moveable(this)) {
     makeAMove(this);
     if (win()) {
      document.getElementById("output").innerHTML = "Congratulations! You win!";
     } else {
      document.getElementById("output").innerHTML = "";
     }
   }
  }

  // make one move for the given tile
  function makeAMove(div) {

   div.id = "square_" + spaceRow + "_" + spaceColumn;
   var divRow = parseInt(div.style.top) / WIDTH;
   var divColumn = parseInt(div.style.left) / WIDTH;

   div.style.top = spaceRow * WIDTH + "px";
   div.style.left = spaceColumn * WIDTH + "px";
   spaceRow = divRow;
   spaceColumn = divColumn;

  }

  // return true if the given tile is moveable
  function moveable(div) {

   var divRow = parseInt(div.style.top) / WIDTH;
   var divColumn = parseInt(div.style.left) / WIDTH;
   if (spaceRow == divRow) {
     return Math.abs(spaceColumn - divColumn) == 1;
   }
   else if (spaceColumn == divColumn) {
     return Math.abs(spaceRow - divRow) == 1;
   }
   else {
     return false;
   }
  }

  // return true if all tiles are at their original positions
  function win() {
   var tiles = document.querySelectorAll(".puzzletile");
   for (var i = 0; i < tiles.length; i++) {
     var row = Math.floor(i / NUM);
     var column = i % NUM;
     if (tiles[i].id != "square_" + row + "_" + column) {
      console.log(tiles[i].id);
      return false;
     }
   }
   return true;
  }
})();