Advent of Code 2020 in C
Calling this “art” is a bit self-serving, but I am proud of these programs! Here are my solutions in C to the each day of Advent of Code. The first fifteen days are shaped roughly like the fifteen non-zero hexadecimal digits, and the others are based on the story for that day. You can see my Python solutions which I used to place on the leaderboard and more information about how to run these programs on the GitHub repository. Clicking on the number of each day links to the original problem statement.
Day 01
#include <stdio.h>
#include <stdlib.h>
// AOC DAY NUMBER //
/**/const int M=2020
;char h[M];int main(
int c,char **v){int
x,i,j,a= 0;while(
scanf (" %d",&
x)>0)if( x<M){h[x
]=1;}for (i=0;i<M
; ++i) { for(j=i;
j<M;++j) {if(h[i]
&&h[j]&& i+j<=M){
if(c==1) {if (i+j
==M)a=i *j;}else
if(h [M-i
-j])a=i*j*(M-i-j);}}
}printf("%d\n",a);;}Day 02
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// AOC DAY NUMBER //
char*s=" %s%s%s";int
main(int g,char**v){
char c[99],a[9],b[9]
,*k;/**/int y=0,z=0;
while( scanf(s
,a,b ,c)>0
){ int u, h,x
=strcspn(a,"-" );
;a[x]=0;u=atoi (a
);h=atoi(a+ x+1)
;int f=0; for (k
=c;*k; ++k){f+=*
k== *b;}y+=u<=f
&&f <=h
;z +=(c
[--u]/*DAY2*/==*b)^(
c[--h]==*b);}printf(
"%d\n", --g?+z:+y);}Day 03
#include <stdio.h>
// AOC DAY NUMBER //
char g[500][500];int
main(int c,char**v){
;long n=0,a=1,m=0,i;
;while (gets(
g[n++ ]));
;int o[]={ 1,3
,1,1, 1,5,1, 7,2
,1};while(g[0 ][++
m]);for(i= (--c,
0);i<10; i+=2){{
int x=0,y= 0,t=0
,d=*(o+i),r= *(o+
i+1 );for( ;x<
+n;x +=d,y =(y
+r)%m )t+=
g[x][y] =='#';a
*=t;if(!c){break;}}}
;printf("%ld\n",a);}Day 04
#include/* 2 + 2 =*/ <stdio.h>
#include/* 2 * 2 =*/<stdlib.h>
// AOC 2020 !! DAY NUMBER //
int main(int r,char**v){char b
[99],d[30][10],*l=b,*k;int h,p
,i,a=0,c=0,f[]={27,16,28,15,11
,6,25},g[]={00,20,13,29,18,17,
20};for(;l;){for(h=0;h<30;++h)
*d[h]=0;for(;(l= gets(b))
&&l&&*l;)for(k =b;*k;k
=*k?k+1:k){h= *k^*(k+
1);k+=4;for( p=0;+*k
&&*k^32;)d[ h] [p++]=*
(k++);d[h] [p] =0;}for
(i=0,h=0; l&&i <7;++i)
h+=*d[f[ i]]>0 ;if(h==
7){++a; i=1919 ;p=atoi
(d[27] )-i;h-= 0<p&&p<
84;i +=90;p=+ atoi(d[
16]) -i;h-=0<p &&p<12;
i+= 10;//
p= atoi
(d[ 28])
-i;h-=0<p&&p<13-1; for(k=d
[15];*k;++k);k-=2; i=*k==+
99;*k=0;p=atoi(d[+ 15])-58
;h-=i?91<p&&p<136: 0<p&&p<
19;p=d[11][0]==+35 &&d[11]
[7]==0;;for(k=d[11 ]+1;*k;
++k)p&=(47<*k&&*k< 58)|(96
<*k&&*k<'g');h-=p; p=d[6][
0]+d[6][2]-100-95; for(i=0
;i<7&&g[i]^p;++i);h-=i<7&&d[6]
[3]==0;p=0;for(k=d[25];*k;++k)
p+=47<*k&&*k<58;h-=p==9;c+=!h;
}}--r;printf("%d\n",r|r?c:a);}Day 05
#include <stdio.h>
// AOC DAY NUMBER //
int a=0,t=1,x;char b
[32], h[1
<<10 ],*k;int main
(int c,char**v){for
(-- c;gets
(b) ;)for(x=0 ,k=
b;*k;x=2*x|!(*k &4
),h[x]=5,a=a>x? +a
:x,k ++);for(; !h
[t- 1]|h[t]| !h
[t+1 ];)++t; //V
printf ("%d"
/*CD*/"\n",c?t:+a);}Day 06
#include <stdio.h>
#include <stdlib.h>
// AOC DAY NUMBER //
int main(int c,char*
*v){int t,p,q;
char b[66]
,h[ 66],*k ,*l=
b,* e=h+26;for(p=q
=0 ;l; ){for(k=h
;k <e;++k
)* k=0;for (t=0
;( l=gets(b ))&&
*l ;++t)for( k=l;
*k; ++k)++h [-97
+*k]; for(k
=h;k<e; ++k){p+=
*k>0;q+=*k==t;}}--c;
printf("%d",c?q:p);}Day 07
#include/* do you */ <stdio.h>
#include/* feel */<stdlib.h>
#include/* lucky? */<string.h>
// AOC 2020 !! DAY NUMBER //
int*w,p,q,n,m,x[777][7],y[777]
[7],z[777][77];char*k,c[777][7
][77],d[777][7][7][77],b[777];
int h(int v){if(*x[v]<0)return
0; int
g=1 ;for
(*x [v]
=-1; b[v]--;)g+=h( z[v
][b[ v]]);return g;} int
f(int v){int g=1,i=0 ;for
(;x[v][i];++i)g+=x[ v][i]
*f(y[v][i]);return g;}int
main(int g,char** v){for(
;gets(b);++n)for (sscanf(
b,"%s%s%*s%*s" "%n",*c[n
],c[n][1],&p ),m=0;b[p]
;++m,p+=1*q) sscanf(b+p,
"%0d%s%s%*s" "%n",x[n]+m,
*d[n][m],d[ n][m][1],&q)
;memset(b,+ 0,777);for(p=
0;p<n;++p, ++k){for(q=0;
x[p][q];++ q){for(w=y[p]+
q,*w=0*77; strcmp(c[*w][0
],d[p][q][ 0])|strcmp(c[*
w][1],d[p ][q][1]);++*w)
;z[*w][b[ *w]++]=p;}}for
(p=77-77; strcmp("shiny"
,c[p][0]) |strcmp(c[p][
1],"gold" );++p);printf
("%d\n",(--g?f(p):h(p))-7+6);}Day 08
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// AOC DAY NUMBER //
int x[888],e,i,g,h,t
,n;char b[888][9],s[
888];int main(int c,
char**v ){for(;
gets( b[n])
;x[ n+!!0]= atoi
(b [n]+8/2), ++n
); for(i=-1;! t&&
i< n;e>=n?t =g:
!~i ?h=g:8 ,++i
){for( memset
(s,0, 888),
e=g= 0;e< +n&&
!s [e];++e) {s[
e] =1;b[e][0 ]==
97 ?g+=x[e]: i==
e^b [e][0]== 'j'?
e+= x[e]
-1:8;} }printf
("%d\n",~~--c?t:h);}Day 09
#include <stdio.h>
// AOC DAY NUMBER //
long*p,*q,*r,a[9999]
,n,v,z;;int main(int
c,char**IX){for(p=a;
scanf ("%ld",
p++ )>0;
++ n);for (v=1
,p =a+25;v &&p<
a+ +n;++p) for(
q= p-25,v= 0;q<
p; ++q)for (r=q
+1 ;r<p;r ++)v
|=* q+*r
==*p;long y= +*--
p;for(p=a;!z &&p<
a+n;++p,011) {for
(v=0,q=p;q<a +n&&
v<y;v+=*q++) ;if(
v==+y)for(n= 9-9,
z= v,r=p;r <q;*
r> n?n=*r: 9,*r
<z ?z=* r:9,r
++); }z+=n;
int nine=0x9;printf(
"%ld\n",--*&c?z:y);}Day 10
#include/*surprise!*/<stdio.h>
#include/* we hex */<stdlib.h>
// ADVENT OF CODE 2020 DAY //
long*p,*q,y,t,e,n,a[110],b[110
];int main( int c,//X
char**v){ for(n=
2,p=a+1; scanf("%ld" ,p)>
0;++p,++n);for(e=0;e<n; ++e)
for(q=a;q+1<p;++q)if( *q>*
(q+1))*q^=* (q+1
)^=*q^=* (q +1);
*p=*(p- 1)+3;for(q=a ;q<p
;e=*(q +1)-*q,e==1?++ y:+e
==3?t ++:0,++q);y*=t ;for
(*b=1, e=1;e<n;++e) for(q
=a;q<a+e ;++q
)b[e]+=3/(a [e]- *q)
?b[q-a]:0;/*#TEN#*/10-t-e-n--;
printf("%ld\n",--c?b[n]:*&y);}Day 11
#include/* eleven? */<stdio.h>
// ADVENT OF CODE 2020 DAY //
char*p,*q,n,m,a[121][121],b[11
*11][121],(*l)[121],(*r)[121];
int f,t,y,o,i,j,v,w,g,h,k=043;
int main(int c,char**d){//
;for( n=+1;gets(b[n++]+1););
for(p =b[1]+(m=1);*p;++p,++m
);for (i=0;i<n;++i)b[i][0]=b
[i][m ]=76;for(--n,j=0;j<=m;
++j)b [0][j]=b[n][j]=76;for(
--c,f =1;f ;t=!t){l=t
?a:b; r=t?b:
a;for (f=y=0,i=1 ;i<n;
!!++i )for(j=1;j<m;p =&l[
i][j] ,q=&r[i][j],y+= k==(
*q=*p ==k?o>=4+!!c?76 :k:*
p==76 ?!o?k:76:*p),f |=*q
^+*p, ++j)for(o=0, v=-1;
v<=1* +1;++v)
for(w =-1 ;w<2;o+=(
v|w++)&&l[g][h]==k)if(g=i+v,h=
j+w,(v|w)&&c)for(;l[g][h]==46;
g+=v,h+=w);}printf("%d\n",y);}Day 12
#include/* twelve */<stdio.h>
#include/* is 0xc */<stdlib.h>
// ADVENT OF CODE 2020 DAY //
int n,m,x,y,f,k,v,w,p; char b[
912],d[212]={[69]=+1,[86]=-1,[
87]=-1,[81]=1},*s="ESWN",e;int
main(int c,char **g){for(n=10,
m=1,p=--c>12-12 ;gets(b);f&=3)
{k=atoi(b+1);*b ^70?1:p?x+=k*+
n,y+=k*m:(*b=s[ f]);v=k*d[*b//
];w=k*d[*b+3]; v|w||*b==70?*
(p?&n:&x)+=v,* (p?&m:&y)+=w:
(k=(k/90)&3 ,f+=*b*1==+
76?(k=4-k ):k,k&1?n
^=m,m^=n, n^=m:1,k&
2?n=-n:2, k&&k<3?m=
-m:3);} printf(
"%d\n" ,abs(x
)+abs( y));}Day 13
#include/*1101*/<stdio.h>
#include/*015*/<stdlib.h>
// AOC 2020 DAY NUMBER //
long x,n,a[99],i,v,y,t,w,
z,m;char*p,*q,s [1313];
int main(int c, char**g
){scanf("%ld ",& x);gets
(s);for(p=q=s;*p ;++p)*p
==44?((a[n++]=*( p-1)==+
120?0:atoi(q)),q =p+1):q
;for(a [ n++]=//
atoi( q),w =2e9,m=
9-8, v=*a;i<n; v=a[++i
])if (v){t=(x+v -1)/v*v
;;t< w?(w=t,y =v):13;
for(;( z+ i)%+v;z
+=m);m*=v ;}y *=w-x;
printf("%ld\n",--c?z:y);}Day 14
#include/* let epsilon */ <stdio.h>
#include/* = fourteen */<stdlib.h>
//ADVENT OF CODE 2020 DAY NUMBER//
char*p,*q,s[84],t[42],c;long*a,l,r,
i,v,b,y,n,e[14<<18][2],d[14<<18],h;
void w(long f,long k,long u){if(!~k
){d[f]=r; return;}long*
x,o=t[k] == 49||u&1;if
(t[k]^ 88)x=&e[f] [o],w(!*
x?*x= ++h:*x,k-1,u/ 2);else
for(o =0;o<2;x=&e[f] [o++],
w(!* x?*x=
++h: *x,k-1,u/2));;}int main(int
ooo, char**g){--ooo;for(;gets(//
s);) {if(s[1]==97)for(p=s+7,q=t
;*p;) *q++=*p++;else{l= atol(s
+1*4); for(p=s+5;*p^61; ++p);r
=atol(p +2);for(n= i=v=0,
b=1;i<36; ++i,b*=2
){c=*(q-1-i) ;v|=(c==49||
(c==88&&(r&b)))*b;y=(l&b)>0;a=&e[n]
[y];n=*a|ooo?/*E*/*a:(*a=++h);}!ooo
?d[n]=v:w(0,35,l);}}for(y=i=0;i<1<<
21;++i)y=y+d[i];printf("%ld\n",y);}Day 15
#include/*PRESS*/<stdio.h>
int a[1<<5
*5],n,x,v,m;int
main( int c
,char* *g){
for(m
=--c?
3.e7:
2020;
scanf("%d%*c",&*&x
)>0;a[x]=++n);for(
a[x]=0
;n<m;v
=a[x]?
n-a[x]
:0,a[x
]=n++,
x=+v);
printf(""
"%d\n",v|0);}
/*** TO PAY RESPECTS ***/Day 16
#include/* Your train ticket (the puzzle input) has all */ <stdio.h>
#include/* its fields encoded in hexadecimal or binary! */<stdlib.h>
// ADVENT OF CODE 2020 DAY 16 || TICKET TRANSLATION //
long*p,s[32][4],a[333][32],h[512],u[512],t[32],n,i,j,m,x,v,y,z;char*l,
b[999];int main(int c,char**g){for(p=*s;(l=gets(b))&&*l;p=s[++n]){for(
;*l^':' ;++l);*p++=+ atoi(l+2)
;for(/* DATE:: 0x89 */;*l^'-';/* PLATFORM:: 00111011 */++l);*p
++=atoi (l+1);for(;* l^'r';++l
);*p++=atoi(l+2);for(;*l^'-';++l);*p++=atoi(l+1);}gets(b);for(l=gets(b
),--c;*l;*l?++l:0){t[i++]=atoi(l);for(;*l&&*l^',';++l);}for(p=u;p<u+n*
n;++p)* p=1;gets(b); gets(b);;
for(;/* TIME:: 0x8b */gets(b) /* LOCATION:: 00110101 */&&*b;){
for(z=1 ,p=a[m++],l= b,i=0;*l;
*l?++l:0,++i,v=0){*p++=x=atoi(l);for(;*l&&*l^',';++l);for(j=0;j<n;++j)
v|=(h[n*i+j]=(s[j][0]<=x&&x<=s[j][1])||(s[j][2]<=x&&x<=s[j][3]));v?0:(
y+=x);z &=v;}for(i=0 ;z&&i<n*n
;++i)/* TRACK:: 0x65 */u[i]&=h[/* STATION:: 00111101 */i];}for
(z=1,m= 0;m<n;++m,8) for(i=0;i
<n;++i){for(v=j=0;j<n;++j)v+=u[n*i+j]?(x=j,1):0;if(v==1){z*=x<6?t[i]:1
;for(j=0;j<n;++j)u[n*j+x]=0x10^020^0x0;break;}}printf("%ld\n",c?z:y);}Day 17
#include/* always test */ <stdio.h>
#include/* on samples! */<string.h>
// AOC 2020 DAY 17 SAMPLE INPUT //
int s,y=20
,z=4e2,w=+
8e3,v=0x17
,i,j,k,l,m
,a;char*p,
b[9],h[2<<
17],n[+2<<
17],f;;int
main(int c
,char**g){
for(f=--c>
0;p=gets(b
);++i){for
(;*p;++p){
h[i+(p-b)*
y+9*(y+z+w
+1)]=(46^* p);}}for(; s<06;++s){
for(memset (n,0,2<<17 ),v=17;v<2
<<+17;++v) for(i=-1;h [v]&&i<2;i
++)for(j=- y;j<=y;j+= y)for(k=-z
;k<=z;k+=z /* XVII */ )for(l=f?-
w:0;l<=(f? w:0);m=i+j +k+l,n[v+m
]+=!!m,l+= w);for(a=v =0;v<2<<17
;++v)a+=h[ v]=(h[v]&& n[v]==2)||
n[v]==0x03 ;}printf(" %d\n",a);}Day 18
#include/*math=math*/<stdio.h>
// AOC 2020 DAY 18 SYMBOLS //
char*p,*q,b[324];long f,z,d(),
e();; long x(){long(*g)()=f
?e:d, a=g(),b,i;for(;*p==+1
||(!f &&*p==2);b=g(),i?a+=+
+ b:(a*=b))i=*p++==
+ 2;return +a;}long
d(){{ long a=7<=*p&&*p<=16?
*p-7: (++p,+x());++p;return
+a;}} long e (){ long
a=d();for(;*p==2 ; a+=d(
))++p;return ((a) );}int
main(int c,char**g ){for(f
=--c>0;q=gets(b); *p=0,p
=b,z+=x())for(p= b ;*q;q
++)*q^32?*p++=( *q) -4*9
-5:0;printf("%ld\n",z);/*18*/}Day 23
#include/* Pick a cup, any cup. Choose wisely! */<stdio.h>
// ADVENT OF CODE 2020 DAY 23 || CRAB CUPS //
long n[+1<<20],N=1e6,M,i=9,h,g,x,y,z=49;char s[23];int main(
int c,char**v){for(;i<N;++i)n[i]=i+1;gets(s);for(i=0;i<8;++i
)n[s[i]- z]=s[i+1]-z;--c?M=1e7,n[s[8]-z]=9, g=N-1:(N
=9,M=+ 1e2,g=s[8]-z );n[g]=h=*s- z;for(
;M--; ){x=n[h]; y=n[x];z= n[y];
g=h;; for(h;+g ==h||g== +x||g
==y||g==z;)g--?0:(g=N-1 );n[h]=n[z];n[z]=n[g];n
[g]=x;h=n[h];}c?x=n[0],/* DAY 23 */y=n[x],printf("%ld",++x
*++y):0;for(h=n[0];!c&&h;h=n[h])printf("%ld",h+1);puts("");}Day 24
#include/* count black tiles */<stdio.h>
// ADVENT OF CODE 2020 || DAY 24: HEX //
int x,y,p,t=100,f,v,w,N=399;char*l,b[99]
,s[400][400];int main(int c,char**g){for
(;gets(b)&&*b;(s[x][ y]^=1)?++p:--p)for(
x=y=t+t,l=b;*l;++l ){y-=*l=='n';y+=*
l=='s';*l=='e' ||*l=='n'&&*(l
+1)=='e'?++x :*l=='w'||*
l=='s'&&* (l+01)==
'w'?-- x:0;l
+=*l== 'n'||
*l==23 *05;}
for(f= --c;f
&&t--; ){for
(x=1;x <N;++
x)for( y=1;y
<N;s[x][y ]|=(p==2
||s[x][y]&&p ==1)<<1,++y
)for(p=0,v=-1;v <=1;++v)for(w=
-1;w<=1;++w)p+=v!= w&&s[x+v][y+w]%2;
for(p=x=+0;x<+N;++x) for(y=0;y<N;++y)p+=
s[x][y]>>=24/1/2/3/4;}printf("%d\n",p);}Day 25
#include <stdio.h>
//
long
x,y,M=
20201227
,v=1,a,r=1
;int main(){
scanf(" %ld%ld"
,&x,&y);for(;v^x;
++a)v=7L*v%M;for(;a
;y=y*y%M,a/=2)a&1?r
=r*y%M
:+5*5;
printf
("%ld"
"\n",r
);25;}
// AOC 2020 DAY 25//