Timings triples, N = 10_000:
  D general: 13.38 s
  Psyco:      6.89 s   (4.12 X)   (1.87 X)
  D1:         4.02 s   (2.40 X)   (1.09 X)
  D2:         3.68 s   (2.20 X)   (1    X)
  C:          1.67 s   (1    X)   (0.45 X)

Triples in [1, 10000): 12467
Triples in [1, 20000): 27171
Triples in [1, 40000): 58728
Triples in [1, 80000): 394138

import std.math: abs, ceil;
import std.intrinsic: bts;
import std.c.stdlib: alloca;
import std.stdio: writefln;

bool jolly(int[] arr) {
  auto flags = new ubyte[arr.length - 1];
  foreach (i, el; arr[0 .. $-1]) {
    auto diff = abs(arr[i+1] - el) - 1;
    if (diff < 0 || diff > arr.length || flags[diff]++)
      return false;
  }
  return true;
}

bool jolly2(int[] arr) {
  int nuints = cast(int)ceil(arr.length / cast(float)(uint.sizeof * 8));
  uint[] flags = (cast(uint*)alloca(nuints * uint.sizeof))[0 .. nuints];
  if (flags.ptr is null)
  	throw new Exception("Stack overflow");
  flags[] = 0;
  foreach (i, el; arr[0 .. $-1]) {
    int diff = abs(arr[i+1] - el) - 1;
    if (diff < 0 || diff > arr.length || bts(flags.ptr, diff))
      return false;
  }
  return true;
}

void main() {
  foreach (a; [[1, 4, 2, 3], [1, 4, 2, -1, 6]])
    writefln(jolly(a), " ", jolly2(a));
}

int editDistance(T)(T[] s1, T[] s2) {
    if (len(s1) > len(s2)) { auto sa = s1; s1 = s2; s2 = sa; }
    auto r1 = range(len(s2) + 1);
    auto r2 = new int[len(r1)];
    foreach (i, c1; s1) {
        r2[0] = i + 1;
        foreach (j, c2; s2)
            r2[j+1] = c1 == c2 ? r1[j] : min(r2[j], r1[j], r1[j+1]) + 1;
        auto ra = r1; r1 = r2; r2 = ra;
    }
    return r1[$ - 1];
}

def editDistanceFast(s1, s2, r1=[0]*35, r2=[0]*35):
    if s1 == s2: return 0
    if len(s1) > len(s2):
        s1, s2 = s2, s1
    len_s2 = len(s2)
    assert len(s2) <= 34, "Error: one input sequence"\
           "is too much long (> 34), use editDistance()."
    for i in xrange(len_s2 + 1):
        r1[i] = i
        r2[i] = 0
    i = 0
    for c1 in s1:
        r2[0] = i + 1
        j = 0
        for c2 in s2:
            if c1 == c2:
                r2[j+1] = r1[j]
            else:
                a1 = r2[j]
                a2 = r1[j]
                a3 = r1[j+1]
                if a1 > a2:
                    if a2 > a3:
                        r2[j+1] = 1 + a3
                    else:
                        r2[j+1] = 1 + a2
                else:
                    if a1 > a3:
                        r2[j+1] = 1 + a3
                    else:
                        r2[j+1] = 1 + a1
            j += 1
        aux = r1; r1 = r2; r2 = aux
        i += 1
    return r1[len_s2]

BENCHMARKS:

recursive, n = 38:
  C: 3.89 s (with __builtin_expect)
  C: 3.99 s
  D: 4.95 s


hash, n = 500_000:
  D:     7.07 s (7.15 s with GC patched)
  D:     5.89 s (GC disabled)
  Psyco: 4.23 s

wordcount, on a txt file of 13_312_768 bytes:
  C: 0.73 s
  D: 5.77 s


gc1, with 6.3 MB of text:
        loading   splitting   total
         time        time     time
  D:       1.87 s     3.58 s   13.76 s
  Python:  0.28 s     1.98 s    3.52 s
  Python:  0.1 s      2.0 s     3.38 s (load with 'rb', same result)
With a Patch to the D GC, plus disabling the GC:
  D:       0.08 s     0.72 s    1.36 s (GC patched + GC disabled after load)


gc2, n=1_000, m=10_000:
               seconds  MB
  DMD class:   18.95    1.7
  GDC class:   17.91    1.8
  DMD struct:  11.77    1.7
  GDC struct:  12.31    1.8
  Python:      37.10    3.1
  Psyco:       15.68    3.5
  Java:         2.19    7.3


gc3 (binarytrees), n = 15:
  Java:   9.12 s
  D:     35.01 s


sort, const n = 1_000_000:
  Random distribution:
    sort: 2.934
    fastSort: 0.881
  Already sorted arrays:
    sort: 1.723
    fastSort: 0.41
 Inverted order arrays:
    sort: 1.853
    fastSort: 0.651

(1 2) (1 3) (1 4) (1 5)
(2 3) (2 4) (2 5)
(3 4) (3 5)
(4 5)

(def subn (n li)
 (if (is 0 n) '(())
     (no li) '()
       (join (map [cons (car li) _] (subn (- n 1) (cdr li)))
             (subn n (cdr li)))))

subn 0 _      = [[]]
subn _ []     = []
subn n (x:xs) = map (x:) (subn (n-1) xs) ++ subn n xs

def subn(n, a):
    if not n: return [[]]
    if not a: return []
    return [[a[0]] + sub for sub in subn(n-1, a[1:])] + subn(n, a[1:])

def subn[T](n: int, li : List[T]) : List[List[T]] = (n,li) match {
   case (0,_)     => List(Nil)
   case (_,Nil)   => Nil
   case (_,x::xs) => (subn(n-1, xs) map (x :: _)) ::: subn(n, xs)
}

import d.func: putr, map, not, range, xrange, select, BaseType, array;

T[][] subn(T)(int n, T[] a) {
    if (!n) return new T[][](1, 0);
    if (not(a)) return new T[][0];
    return map((T[] s){return a[0..1] ~ s;}, subn(n-1, a[1..$])) ~ subn(n, a[1..$]);
}

T[][] subn2(T)(int n, T[] a) {
    if (!n) return new T[][](1, 0);
    if (not(a)) return new T[][0];
    T[] s;
    return select(a[0..1] ~ s, s, subn2(n-1, a[1..$])) ~ subn2(n, a[1..$]);
}

BaseType!(TyIter)[][] subn3(TyIter)(int n, TyIter iter) {
    auto a = array(iter);
    alias BaseType!(TyIter) T;
    if (!n) return new T[][](1, 0);
    if (not(a)) return new T[][0];
    return map((T[] s){return a[0..1] ~ s;}, subn3(n-1, a[1..$])) ~ subn3(n, a[1..$]);
}

void main() {
    putr( subn(2, range(5)) );
    // Output: [[0, 1], [0, 2], [0, 3], [0, 4], [1, 2], [1, 3], [1, 4],
    //          [2, 3], [2, 4], [3, 4]]  

    putr( subn2(3, range(5)) );
    // [[0, 1, 2], [0, 1, 3], [0, 1, 4], [0, 2, 3], [0, 2, 4], [0, 3, 4],
    //  [1, 2, 3], [1, 2, 4], [1, 3, 4], [2, 3, 4]]

    putr( subn3(2, xrange(5)) );
    // Output: [[0, 1], [0, 2], [0, 3], [0, 4], [1, 2], [1, 3], [1, 4],
    //          [2, 3], [2, 4], [3, 4]]    
}

struct A003714 {
  void generator() {
    yield(1);
    foreach(x; A003714()) {
      yield(2 * x);
      if (!(x & 1))
        yield(2 * x + 1);
    }
  }
  mixin Generator!(int);
}

def A003714():
  yield 1
  for x in A003714():
    yield 2 * x
    if not (x & 1):
      yield 2 * x + 1

import array

def main(m):
  lens = array.array('H', [0]) * m
  max_steps = max_steps_pos = 1
  for i in xrange(1, m):
    n = i
    n_steps = 1
    while n != 1:
      if n < i:
        n_steps += lens[n] - 1
        break
      n = 3 * n + 1 if n & 1 else n // 2
      n_steps += 1
    if n_steps > max_steps:
      max_steps = n_steps
      max_steps_pos = i
    lens[i] = n_steps
  return max_steps, max_steps_pos

import psyco; psyco.bind(main)
print "max_steps, max_steps_pos:", main(1000000)

import std.stdio, std.c.stdlib;

void main() {
  const uint m = 1_000_000;
  auto lens = (cast(ushort*)malloc(m * ushort.sizeof))[0 .. m];
  uint max_steps = 1;
  uint max_steps_pos = 1;

  for (uint i = 1; i < m; i++) {
    uint n = i;
    uint n_steps = 1;

    while (n != 1) {
      if (n < i) {
        n_steps += lens[n] - 1;
        break;
      }
      n = n & 1 ? 3 * n + 1 : n / 2;
      n_steps++;
    }
    if (n_steps > max_steps) {
      max_steps = n_steps;
      max_steps_pos = i;
    }
    lens[i] = n_steps;
  }
  writefln("max_steps, max_steps_pos: ", max_steps, " ", max_steps_pos);
}


Timings:
m = 1_000_000:
D/C:    0.29 s  ( 1   X)
Psyco:  1.60 s  ( 5.5 X) with array 'H'
Python: 19.20 s (66   X) with list

#include "stdio.h"
#include "assert.h"

int main(int argc, char** argv) {
    int value = 2;
    if (argc == 2)
        value = atoi(argv[1]);
    assert(value >= 0 && value <= 2);

    const void *labels[] = {&&VAL0, &&VAL1, &&VAL2};

    goto *labels[value];
    assert(0);

    VAL0:
        puts("The value is 0");
        goto END;
    VAL1:
        puts("The value is 1");
        goto END;
    VAL2:
        puts("The value is 2");
        goto END;
    END:
        return 0;
}

...
LC1:
	.ascii "value >= 0 && value <= 2\0"
LC2:
	.ascii "The value is 0\0"
LC3:
	.ascii "The value is 1\0"
LC4:
	.ascii "The value is 2\0"
...

...
	call	__assert   ; corrisponde alla riga assert(0);
L6:
	movl	$L7, -20(%ebp)
	movl	$L8, -16(%ebp)
	movl	$L9, -12(%ebp)
	movl	-8(%ebp), %eax
	movl	-20(%ebp,%eax,4), %eax
	jmp	*%eax
L7:
	movl	$LC2, (%esp)
	call	_puts
	jmp	L10
L8:
	movl	$LC3, (%esp)
	call	_puts
	jmp	L10
L9:
	movl	$LC4, (%esp)
	call	_puts
L10:
	movl	$0, %eax
	addl	$36, %esp
	popl	%ecx
	popl	%ebp
	leal	-4(%ecx), %esp
	ret
...

switch (value) {
    case 0:
        puts("The value is 0");
        break;
    case 1:
        puts("The value is 1");
        break;
    case 2:
        puts("The value is 2");
        break;
}
return 0;

switch (*p1++) {
    case '1': goto S1;
    case '2': goto S2;
    case '3': goto S3;
}

goto *labelsS123[*p1++ - '1'];

const void *labelsS123[] = {&&S1, &&S2, &&S3};

p1 = p2 = 0
pend = len1
S0, S1, S2, S3, S11, S22, S33, END = xrange(8)
state = S0

while True:
    if state == S0:
        if p1 == pend: state = END
        elif s1[p1] == "1": p1 += 1; state = S1
        elif s1[p1] == "2": p1 += 1; state = S2
        elif s1[p1] == "3": p1 += 1; state = S3

    elif state == S1:
        if p1 == pend: s2[p2] = '1'; p2 += 1; s2[p2] = '1'; p2 += 1; state = END
        elif s1[p1] == "1": p1 += 1; state = S11
        elif s1[p1] == "2": p1 += 1; s2[p2] = '1'; p2 += 1; s2[p2] = '1'; p2 += 1; state = S2
        elif s1[p1] == "3": p1 += 1; s2[p2] = '1'; p2 += 1; s2[p2] = '1'; p2 += 1; state = S3
...