import tango.io.Stdout; /** * SICP練習2.29。 */ class Mobile { Branch left; Branch right; this(Branch l, Branch r) { left = l; right = r; } } class Structure { int weight = -1; Mobile child; this(int w, Mobile c) { weight = w; child = c; } } class Branch { int length; Structure str; this(int len, Structure s) { length = len; str = s; } } // b、総重量を求める int strWeight(Structure s) { if (s.child !is null) { return strWeight(s.child.left.str) + strWeight(s.child.right.str); } return s.weight; } int totalWeight(Mobile m) { return strWeight(m.left.str) + strWeight(m.right.str); } // c、バランスかどうか bool isBalance(Mobile m) { bool balance; Branch left = m.left; Branch right = m.right; Structure ls = left.str; Structure rs = right.str; // child is balance? Mobile lc = ls.child; if (lc !is null) { balance = isBalance(lc); if (!balance) { return false; } } Mobile rc = rs.child; if (rc !is null) { balance = isBalance(rc); if (!balance) { return false; } } // self is balance? int lt = left.length * strWeight(ls); int rt = right.length * strWeight(rs); return lt == rt; } void main() { // build a balance mobile Structure s1 = new Structure(1, null); Structure s2 = new Structure(2, null); Structure s3 = new Structure(4, null); Structure s4 = new Structure(8, null); Branch b1 = new Branch(8, s1); Branch b2 = new Branch(4, s2); Branch b3 = new Branch(2, s3); Branch b4 = new Branch(1, s4); Mobile m1 = new Mobile(b1, b2); Mobile m2 = new Mobile(b3, b4); Structure sa = new Structure(-1, m1); Structure sb = new Structure(-1, m2); Branch ba = new Branch(4, sa); Branch bb = new Branch(1, sb); Mobile root = new Mobile(ba, bb); // b int tw = totalWeight(root); Stdout.formatln("total weight is: {}", tw); // c bool balance = isBalance(root); Stdout.formatln("balance = {}", balance); }