c-gcc, 88 bytes

Result

AC

Duration

729ms

Code [DL]

b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}

stdin

                   T                              
                                                  
                                                  
                                                  
                                                  
                                                  
          K                                       

stdout

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          cccccccccc                              

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'b' [-Wimplicit-int]
/tmp/code.c:1:3: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
   ^
/tmp/code.c:1:5: warning: return type defaults to 'int' [-Wimplicit-int]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
     ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:5: warning: type of 'd' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:22: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
                      ^~~~~~~
/tmp/code.c:1:22: note: 'getchar' is defined in header '<stdio.h>'; did you forget to '#include <stdio.h>'?
+#include <stdio.h>
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
                      ^~~~~~~
/tmp/code.c:1:34: warning: operation on 'd' may be undefined [-Wsequence-point]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
                                 ~^~~~~~~
/tmp/code.c:1:59: warning: suggest parentheses around arithmetic in operand of '|' [-Wparentheses]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
                                                          ~^~
/tmp/code.c:1:67: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 b,c;main(d){for(;~(c=getchar());d=++d%51){if(c==84)d=0;b=c&1|b&&d;putchar(!d||b?99:c);}}
                                                                   ^~~~~~~

strace