2008-11-18 长距离打车如何省钱？

学JavaScript的时候写的一个用于在长距离打车时，计算多远抬一次表最省钱的抬表方案的小程序，参数可以根据需要随意修改。
X轴是距离，Y轴是费用，不同的颜色表示不同的抬表方案
大致的简单结论是20公里以上的时候，每15公里抬一次表，能省出10%左右吧。
 下面代码存为taxi.html，然后打开即可在浏览器中看到结果。
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<html>
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<script type="text/javascript" src="http://www.walterzorn.com/scripts/wz_jsgraphics.js"></script>
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​
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<body>
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<script type="text/javascript">
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<!--
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function getPrice(distance, night) {
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    var unitPrice = 2.0,
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    basicDistance = 3,
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    basicPrice = 10,
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    extDistance = 15,
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    extPrice = 3.0;
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​
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    var price = 0.0;
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    if ( distance == 0 ) return 0;
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    if ( distance <= basicDistance ) return basicPrice;
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​
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    if ( distance <= extDistance ) {
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        price = basicPrice + unitPrice * (distance - basicDistance);
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        return price;
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    }
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​
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    price += basicPrice + unitPrice*(extDistance-basicDistance) + extPrice*(distance-extDistance)
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    return price;
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}
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​
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function getPriceWithReset(distance, night, reset) {
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    if ( reset == 0 ) {
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        return getPrice(distance, night);
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    } else {
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        return getPrice(reset, night) * Math.floor(distance/reset) + getPrice(distance % reset, night);
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    }
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}
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​
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var coordXUnit = 8, coordYUnit = 3,
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basicX = 100, basicY = 50,
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coordMaxX = 101, coordMaxY = 251;
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​
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function drawString(str, x, y) {
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    jg.drawString(str, basicX+x*coordXUnit, basicY+(coordMaxY-y)*coordYUnit);
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}
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​
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function drawPoint(x, y) {
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    drawLine(x, y, x, y);
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}
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​
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function drawLine(x1, y1, x2, y2) {
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    jg.drawLine(basicX + x1*coordXUnit, basicY + (coordMaxY-y1)*coordYUnit, basicX + x2*coordXUnit, basicY + (coordMaxY-y2)*coordYUnit);
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}
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​
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function drawPolyline(ax, ay) {
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    var axx = new Array(), ayy = new Array();
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​
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    for (var e in ax) {
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        axx.push(basicX + (ax[e] * coordXUnit) );
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    }
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​
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    for (var e in ay) {
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        ayy.push(basicY + (coordMaxY - ay[e])*coordYUnit);
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    }
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​
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    jg.drawPolyline(axx, ayy);
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}
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​
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function drawCoordinate() {
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    jg.setColor("#ee8800");
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    drawLine(0, 0, coordMaxX, 0);
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    drawLine(0, 0, 0, coordMaxY);
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​
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    drawString(0, -2, -2);
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    for (var i = 1; i < coordMaxX; i++) {
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        if (i%5==0) {
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            // draw grid
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            jg.setStroke(Stroke.DOTTED);
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            drawLine(i, 0, i, coordMaxY);
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            // draw mark
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            jg.setStroke(0);
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            drawLine(i, 0, i, -2);
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            drawString(i, i-1, -3);
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        } else {
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            drawLine(i, 0, i, -1);
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        }
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    }
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​
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    for (var i = 1; i < coordMaxY ; i++) {
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        if (i%5==0) {
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            // draw grid
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            jg.setStroke(Stroke.DOTTED);
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            drawLine(0, i, coordMaxX, i);
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            // draw mark
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            jg.setStroke(0);
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            drawLine(0, i, -2, i);
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            drawString(i, -7, i+1);
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        } else {
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            drawLine(0, i, -1, i);
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        }
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    }
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}
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​
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function drawPriceLine(night, reset) {
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    var ax = new Array(), ay = new Array();
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​
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    for (var d=0; d<70; d++) {
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        ax.push(d);
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        ay.push(getPriceWithReset(d, 0, reset));
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    }
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    drawPolyline(ax, ay);
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}
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​
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/////////////// main section ///////////////
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var jg = new jsGraphics();
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jg.setFont("verdana,geneva,sans-serif", "10px", Font.PLAIN);
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​
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drawCoordinate();
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drawString("reset:", 0, -10);
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jg.setColor("#000000");
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drawPriceLine(0, 0);
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drawString("0", 5, -10);
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jg.setColor("#FF0000");
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drawPriceLine(0, 10);
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drawString("10", 10, -10);
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jg.setColor("#00FF00");
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drawPriceLine(0, 15);
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drawString("15", 15, -10);
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jg.setColor("#0000FF");
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drawPriceLine(0, 20);
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drawString("20", 20, -10);
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​
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///////////////// from wangjing to my home, 35KM /////////////////
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jg.setColor("#880000");
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var xp = new Array(), yp = new Array();
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for ( var i=10; i<30; i++) {
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    xp.push(i);
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    yp.push(getPriceWithReset(35, 0, i));
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}
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drawPolyline(xp, yp);
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​
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drawString(getPriceWithReset(35, 0, 15), 0, -20);
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jg.paint();
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//-->
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</script>
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</body>
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</html>
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