An introduction to the graphic and text code for implementing the eight-digit heuristic A* algorithm animation effect on web pages using JavaScript-JS Tutorial-php.cn

This article mainly introduces the use of JavaScript to implement the eight-digit heuristic A* algorithm animation effect on the web page. Friends in need can refer to the

recent artificial The teacher in the smart class arranged an eight-digit experiment. I saw many eight-digit heuristic A* algorithms on the Internet, but most of them were implemented on the console using C or C++, so I used js to implement it on the web page. Made a similar one in .

First of all, the eight-digit number is a nine-square grid, with one space in it, and the other eight corresponding numbers 1-8.

Move the space so that the last The state is ordered, as shown below

The heuristic algorithm refers to using the heuristic function to remove solution nodes that do not comply with the rules when solving removed to reduce the solution space of the problem.

The A* algorithm is a heuristic algorithm that uses an evaluation function. In this example, the number of grids that differ between the current node state and the final node state is used to evaluate the quality of the node, and the superior node is stored and used later. Expand and discard inferior nodes.

Use the web to achieve this. First, add nine input text boxes as shown in the figure in the html. The background picture is a digital grid

The page code is

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>八数码</title>
 <style type="text/css">
 #result input{
  display: inline-block;
  font-family:"微软雅黑";
  font-size: 60px;
  font-weight: 900;
  text-align: center;
  width:100px;
  height:100px;
  background:url(images/0.png);
  background-size:cover;
 }
</style>
</head>
<body>
 <p id="result">
  <input type="text" id="r1">
  <input type="text" id="r2">
  <input type="text" id="r3"><br>
  <input type="text" id="r4">
  <input type="text" id="r5">
  <input type="text" id="r6"><br>
  <input type="text" id="r7">
  <input type="text" id="r8">
  <input type="text" id="r9"><br>
 </p>
 <button onclick="run()">求解</button>
</body>
</html>

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Then use javascript to get the input value and save it in two-dimensional array

var startArray=[[8,1,3],[0,2,4],[7,6,5]];//初始化八数码数组
   //获取输入的初始状态
   var cpic=1;
   for(var i=0;i<N;i++){
    for(var j=0;j<N;j++){
     var rid=&#39;r&#39;+cpic++;
     var inputValue=getId(rid).value;
     if(inputValue==""){inputValue=0;}
     startArray[i][j]=parseInt(inputValue);
     getId(rid).value="";
    }
   }
var startGraph=new Graph(startArray);
var endArray=[[ 1,2,3],[ 8,0,4 ],[ 7,6,5 ]];
var endGraph=new Graph(endArray);//目标节点
evaluateGraph(startGraph,endGraph);
showGraph(startGraph);

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The Graph class is used to save a state Node related data:

//节点类
  var Graph = function(formData){
   this.form=formData;
   this.evalue=0;
   this.udirect=0;
   this.parent=null;
  };

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Implement a showGraph() function to display the eight-digit status:

function showGraph(graph) {
   var c=1;
   for(var i=0;i<N;i++){
    for(var j=0;j<N;j++){
     var s=&#39;r&#39;+c++;
     getId(s).style.backgroundImage="url(images/"+graph.form[i][j]+".png)";
    }
   }
  }

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Use the evaluation function evaluateGraph() to evaluate the gap value between the current node and the target node

//评估函数
  function evaluateGraph(theGraph, endGraph){
   var differ = 0;//差距数
   for (var i = 0; i<N; i++)
   {
    for (var j = 0; j<N; j++)
    {
     if (theGraph.form[i][j] != endGraph.form[i][j]){differ++;}
    }
   }
   theGraph.evalue = differ;
   return differ;
  }

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Use the moveGraph() function to move and return a new node:

//移动数码组
  function moveGraph(theGraph, direct){
   var HasGetBlank = 0;//是否找到空格位置
   var AbleMove = 1;//是否可移动
   var i, j, t_i, t_j;
   //查找空格坐标i,j
   for (i = 0; i<N; i++)
   {
    for (j = 0; j<N; j++)
    {
     if (theGraph.form[i][j] == 0)
     {
      HasGetBlank = 1;
      break;
     }
    }
    if (HasGetBlank == 1)
     break;
   }
   t_i = i;
   t_j = j;
   //移动空格
   switch (direct)
   {
    case 1://上
     t_i--;
     if (t_i<0)
      AbleMove = 0;//移动超过边界
     break;
    case 2://下
     t_i++;
     if (t_i >= N)
      AbleMove = 0;
     break;
    case 3://左
     t_j--;
     if (t_j<0)
      AbleMove = 0;
     break;
    case 4://右
     t_j++;
     if (t_j >= N)
      AbleMove = 0;
     break;
   }
   //Direct方向不能移动，返回原节点
   if (AbleMove == 0)
   {
    return theGraph;
   }
   //向Direct方向移动，生成新节点
   var ta=[[0,0,0],[0,0,0],[0,0,0]];
   var New_graph = new Graph(ta);
   for (var x = 0; x<N; x++)//复制数码组
   {
    for (var y = 0; y<N; y++)
    {
     New_graph.form[x][y] = theGraph.form[x][y];
    }
   }
   //交换
   New_graph.form[i][j] = New_graph.form[t_i][t_j];//交换空格和移动方向上的数字
   New_graph.form[t_i][t_j] = 0;
   return New_graph;
  }

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Finally, the search function searches downward layer by layer starting from the initial node until it reaches the target node. Return to the child node and trace back to the parent node layer by layer from the child node to find the solution path:

//搜索路径
  function Search(beginGraph, endGraph){
   var g1, g2, g;
   var Step = 0;//深度
   var Direct = 0;//方向
   var i;
   var front=-1,rear=-1;
   g1=beginGraph;//初始八数码节点
   while (g1)//队列不空,从close队列中拿出一个节点
   {
    for (i = 1; i <= 4; i++){//分别从四个方向推导出新子节点
     Direct = i;
     if (Direct == g1.udirect)
      continue;//跳过屏蔽方向
     g2=moveGraph(g1,Direct);
     if (evaluateGraph(g2,g1)!=0){//数码组是否可以移动
      evaluateGraph(g1,endGraph);
      evaluateGraph(g2,endGraph);//评价新的节点
      if (g2.evalue <= g1.evalue + 1)//利用评估值判断是否为优越节点
      { //若为优，将g2的父节点指向g1
       g2.parent = g1;
       //设置屏蔽方向，防止往回推
       switch (Direct){
        case 1://上
         g2.udirect = 2;
         break;
        case 2://下
         g2.udirect = 1;
         break;
        case 3://左
         g2.udirect = 4;
         break;
        case 4://右
         g2.udirect = 3;
         break;
       }
       Qu[++rear]=g2;//把优越节点放到close队列
       if (g2.evalue == 0)//为0则搜索完成
       {
        g = g2;
        break;
       }
      }
      else{g2 = null;}//抛弃劣质节点
     }
    }
    //搜索完成，继续退出
    if (typeof g !== &#39;undefined&#39;)
    {
     if (g.evalue == 0)
     {
      break;
     }
    }
    Step++;//统计深度
    if (Step>Max_Step){
     alert("超过搜索深度！");
     break;}
    g1=Qu[++front];//从close队列中拿出一个节点继续下一轮展开
   }
   return g;
  }

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Finally, push the solution path nodes into the stack in order, and pop up one node every second to display and form an animation:

var top=-1;
   var G;
   G = Search(startGraph, endGraph);
   //解序列存入堆栈
   var P=G;
   while (P != null)
   {
    top++;
    St[top] = P;
    P = P.parent;
   }
   //动画执行
   var si=setInterval(function () {
    if (top>-1)
    {
     showGraph(St[top]);
     top--;
    }else {
     clearInterval(si);
    }
   },1000);
  }

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