今年Google笔试用Code Jam。今天试试怎么用。这东西很威武啊，支持各种语言，只要免费许可的都可以，还可以下载别人提交的code。做了几个非常简单的，结果就遇到坑了。

第一道题很简单，将一些字母数字的组合翻译成十进制，类似IEEE754的float格式。需要注意的是，使得到的数字最小，则首位字符对应0，第2个与首位不同的字符对应0。

public long readFormat(String s) {    int[] map = new int[256];    int used = 0;    for (int i = 0; i < s.length(); i++) {        char c = s.charAt(i);        if (map[c] == 0) {        used++;        map[c] = used;        }    }    int radix = used;    if (radix == 1)        radix = 2;    long ret = 0;    for (int i = 0; i < s.length(); i++) {        char c = s.charAt(i);        int num = map[c];        if (num == 1) {        } else if (num == 2) {        num = 0;        } else {        num--;        }        ret *= radix;        ret += num;    }    return ret;}void run() {    int COUNT = sc.nextInt();    for (int c = 0; c < COUNT; c++) {        String s = sc.next();        System.out.println(String.format("Case #%d: %d", c + 1,            readFormat(s)));    }}

第二道是几何问题，也不难。最后计算长度的时候遇到问题。这个长度可以用速度乘以时间算出来，同时这个长度也是直角三角形的一个边，也可以根据勾股定律用另两条边求出来。我按照第一个方法提交失败，按照第二个方法，就成功了。

class Pos {    double x, y, z;    public Pos() {    }    public Pos(int x, int y, int z) {        this.x = x;        this.y = y;        this.z = z;    }    public void add(Pos p) {        this.x += p.x;        this.y += p.y;        this.z += p.z;    }    public void divide(double d) {        this.x /= d;        this.y /= d;        this.z /= d;    }    public double multiply(Pos p) {        return this.x * p.x + this.y * p.y + this.z * p.z;    }    public Pos multiply(double d) {        this.x *= d;        this.y *= d;        this.z *= d;        return this;    }    public double getDistanceSqare() {        return x * x + y * y + z * z;    }    public double getDistance() {        debug(getDistanceSqare());        return sqrt(getDistanceSqare());    }}class Fly {    Pos p = new Pos();    Pos v = new Pos();    public void add(Fly fl) {        p.add(fl.p);        v.add(fl.v);    }    public void divide(int d) {        p.divide(d);        v.divide(d);    }    @Override    public String toString() {        return "x: " + p.x + " y: " + p.y + " z: " + p.z + " vx: " + v.x                + " vy: " + v.y + " vz: " + v.z;    }}void run() {    int COUNT = sc.nextInt();    for (int c = 0; c < COUNT; c++) {        int cc = sc.nextInt();        Fly center = new Fly();        for (int i = 0; i < cc; i++) {            Fly fl = new Fly();            fl.p.x = sc.nextInt();            fl.p.y = sc.nextInt();            fl.p.z = sc.nextInt();            fl.v.x = sc.nextInt();            fl.v.y = sc.nextInt();            fl.v.z = sc.nextInt();            center.add(fl);        }        center.divide(cc);        debug(center);        double dotResult = -center.p.multiply(center.v);        double distance = 0;        double time = 0;        if (dotResult <= Double.MIN_VALUE) {            distance = center.p.getDistance();        } else {            double vDisSqare = center.v.getDistanceSqare();            time = dotResult / vDisSqare;            distance = center.p.getDistanceSqare()                    - center.v.getDistanceSqare() * time * time;            if (distance < 0)                distance = 0;            else                distance = sqrt(distance);        }        System.out.println(String.format("Case #%d: %.8f %.8f", c + 1,            distance, time));    }}