20151023 － 用天枰3次从12个球中找1个不等重球的问题

if a1+a2+a3+a4 == b1+b2+b3+b4 : // x in c1 c2 c3 c4
    if c1+c2 == a1+a2 : // x in c3 c4
        if c3 == a3 :
            c4 is x
        else c3 != a3 :
            c3 is x
    elif c1+c2 != a1+a2 : // x in c1 c2
        if c1 == a1 :
            c2 is x
        else c1 != a1 :
            c1 is x
elif a1+a2+a3+a4 != b1+b2+b3+b4 : // x in a b
    // reset a = heavier ...
    if a1+a2+a3+b1+b2 == c1+c2+c3+c4+a4 : // x in b3 b4
        if b3 == c1 :
            b4 is x
        else b3 != c1 :
            b3 is x
    elif a1+a2+a3+b1+b2 > c1+c2+c3+c4+a4 : // x in a1 a2 a3
        if a1 == a2 :
            a3 is x
        else a1 < a2 :
            a2 is x
        else a1 > a2 :
            a1 is x
    elif a1+a2+a3+b1+b2 < c1+c2+c3+c4+a4 : // x in b1 b2 a4
        if b1 == b2 :
            a4 is x
        else b1 > b2 :
            b2 is x
        else b1 < b2 :
            b1 is x