Question

只是为了好玩，我正在创建旅行商问题的基本 JavaScript 实现。

它基本上会创建一个具有随机坐标的城市数组，将它们绘制在画布上，然后显示它们之间的路径。然后我有一个按钮可以启动“findBetterRoute”功能，它只是交换两个城市，如果路径更好，它将返回新路线，如果更糟，它将返回原始路线。但是，我发现最后一部分不起作用 - 它有时会绘制一条比原始路线更长的路线，而我终生无法理解我做错了什么。

这是我的代码：

<html>

<head>
  <title>The Traveling Salesman Problem</title>
</head>

<body onload="drawInitial()">
  <canvas id="TSP" width="1000" height="1000" style="border:1px solid #000000;"></canvas>
  <script>
    var canvas = document.getElementById("TSP");
    var ctx = canvas.getContext("2d");
    var numberofCities = 5;
    let city = [numberofCities];

    for (i = 0; i < numberofCities; i++) {
      city[i] = [Math.random() * 1000 + 1, Math.random() * 1000 + 1];
    }

    function drawInitial() {
      drawPath(city);
    }

    function drawPath(cityarray) {
      ctx.moveTo(cityarray[0][0], cityarray[0][1]);
      for (i = 0; i < cityarray.length; i++) {
        if (i != 0) {
          ctx.lineTo(cityarray[i][0], cityarray[i][1]);
          ctx.stroke();
        }
        ctx.beginPath();
        ctx.arc(cityarray[i][0], cityarray[i][1], 2, 0, Math.PI * 2, true);
        ctx.fill();
      }
      ctx.lineTo(city[0][0], city[0][1]);
      ctx.stroke();
      ctx.font = "30px Arial";
      ctx.fillText("Path Length: " + parseInt(calculatePathLength(city)), 10, 50);
    }

    function calculatePathLength(cityarray) {
      let pathLength = 0;
      for (i = 0; i < (cityarray.length - 1); i++) {
        pathLength = pathLength + Math.sqrt((Math.pow((cityarray[i][0] - cityarray[i + 1][0]), 2)) + (Math.pow((cityarray[i][1] - cityarray[i + 1][1]), 2)))
      }
      pathLength = pathLength + Math.sqrt((Math.pow((cityarray[numberofCities - 1][0] - cityarray[0][0]), 2)) + (Math.pow((cityarray[numberofCities - 1][1] - cityarray[0][1]), 2)))
      return pathLength;
    }

    function swap2RandomCities(cityarray) {
      var city1 = 1;
      var city2 = 2;
      do {
        city1 = parseInt(Math.random() * numberofCities);
        city2 = parseInt(Math.random() * numberofCities);
      } while (city1 == city2);
      var swapArray = [];
      swapArray[0] = [cityarray[city1][0], cityarray[city1][1]];
      swapArray[1] = [cityarray[city2][0], cityarray[city2][1]];
      cityarray[city1] = swapArray[1];
      cityarray[city2] = swapArray[0];
      return cityarray;
    }

    function findBetterRoute(cityArray) {
      var currentlength = calculatePathLength(cityArray);
      var newRoute = swap2RandomCities(cityArray);
      if (calculatePathLength(newRoute) < currentlength) {
        return newRoute;
      } else {
        return cityArray;
      }
    }

    function ButtonClick() {
      city = findBetterRoute(city);
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      drawPath(city);
    }
  </script>
  <button onclick="ButtonClick()">Find Better Route</button>
</body>

</html>

TSP 实现似乎忽略了 if 语句

0 个答案: