Submission #4036015

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Source Code Expand

import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}

const mod = 10^^9+7;
alias mint = FactorRing!mod;

void main()
{
  int h, w, k; readV(h, w, k);

  int[] b;
 loop: foreach (i; 0..1<<(w-1)) {
    foreach (j; 0..w-2)
      if (i.bitTest(j) && i.bitTest(j+1))
        continue loop;
    b ~= i;
  }

  auto dp = new mint[][](h+1, w);
  dp[0][0] = 1;
  foreach (i; 0..h)
    foreach (j; 0..w)
      foreach (bi; b) {
        if (j > 0 && bi.bitTest(j-1)) dp[i+1][j-1] += dp[i][j];
        else if (j < w-1 && bi.bitTest(j)) dp[i+1][j+1] += dp[i][j];
        else dp[i+1][j] += dp[i][j];
      }

  writeln(dp[h][k-1]);
}

pragma(inline) {
  pure bool bitTest(T)(T n, size_t i) { return (n & (T(1) << i)) != 0; }
  pure T bitSet(T)(T n, size_t i) { return n | (T(1) << i); }
  pure T bitReset(T)(T n, size_t i) { return n & ~(T(1) << i); }
  pure T bitComp(T)(T n, size_t i) { return n ^ (T(1) << i); }

  pure T bitSet(T)(T n, size_t s, size_t e) { return n | ((T(1) << e) - 1) & ~((T(1) << s) - 1); }
  pure T bitReset(T)(T n, size_t s, size_t e) { return n & (~((T(1) << e) - 1) | ((T(1) << s) - 1)); }
  pure T bitComp(T)(T n, size_t s, size_t e) { return n ^ ((T(1) << e) - 1) & ~((T(1) << s) - 1); }

  import core.bitop;
  pure int bsf(T)(T n) { return core.bitop.bsf(ulong(n)); }
  pure int bsr(T)(T n) { return core.bitop.bsr(ulong(n)); }
  pure int popcnt(T)(T n) { return core.bitop.popcnt(ulong(n)); }
}

struct FactorRing(int m, bool pos = false)
{
  version(BigEndian) union { long vl; struct { int vi2; int vi; } } else union { long vl; int vi; }
  alias FR = FactorRing!(m, pos);
  @property static init() { return FR(0); }
  @property int value() { return vi; }
  @property void value(int v) { vi = mod(v); }
  alias value this;

  this(int v) { vi = v; }
  this(int v, bool runMod) { vi = runMod ? mod(v) : v; }
  this(long v) { vi = mod(v); }

  ref auto opAssign(int v) { vi = v; return this; }

  pure auto mod(int v) const { static if (pos) return v%m; else return (v%m+m)%m; }
  pure auto mod(long v) const { static if (pos) return cast(int)(v%m); else return cast(int)((v%m+m)%m); }

  static if (!pos) pure ref auto opUnary(string op: "-")() { return FR(mod(-vi)); }

  static if (m < int.max / 2) {
    pure ref auto opBinary(string op)(int r) if (op == "+" || op == "-") { return FR(mod(mixin("vi"~op~"r"))); }
    ref auto opOpAssign(string op)(int r) if (op == "+" || op == "-") { vi = mod(mixin("vi"~op~"r")); return this; }
  } else {
    pure ref auto opBinary(string op)(int r) if (op == "+" || op == "-") { return FR(mod(mixin("vl"~op~"r"))); }
    ref auto opOpAssign(string op)(int r) if (op == "+" || op == "-") { vi = mod(mixin("vl"~op~"r")); return this; }
  }
  pure ref auto opBinary(string op: "*")(int r) { return FR(mod(vl*r)); }
  ref auto opOpAssign(string op: "*")(int r) { vi = mod(vl*r); return this; }

  pure ref auto opBinary(string op)(ref FR r) if (op == "+" || op == "-" || op == "*") { return opBinary!op(r.vi); }
  ref auto opOpAssign(string op)(ref FR r) if (op == "+" || op == "-" || op == "*") { return opOpAssign!op(r.vi); }
}

Submission Info

Judge Result