Find prime n such that reversed n is also prime: Difference between revisions
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(Added Forth solution) |
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167 179 181 191 199 311 313 337 347 353 |
167 179 181 191 199 311 313 337 347 353 |
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359 373 383 389 |
359 373 383 389 |
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</pre> |
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=={{header|Forth}}== |
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{{works with|Gforth}} |
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<lang forth>: prime? ( n -- ? ) here + c@ 0= ; |
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: not-prime! ( n -- ) here + 1 swap c! ; |
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: prime-sieve ( n -- ) |
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here over erase |
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0 not-prime! |
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1 not-prime! |
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2 |
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begin |
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2dup dup * > |
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while |
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dup prime? if |
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2dup dup * do |
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i not-prime! |
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dup +loop |
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then |
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1+ |
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repeat |
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2drop ; |
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: reverse ( n -- n ) |
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0 swap |
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begin |
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dup 0 > |
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while |
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10 /mod swap rot 10 * + swap |
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repeat drop ; |
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: main |
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1000 prime-sieve |
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0 |
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500 1 do |
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i prime? if i reverse prime? if |
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1 + |
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i 3 .r |
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dup 10 mod 0= if cr else space then |
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then then |
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loop |
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cr ." Count: " . cr ; |
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main |
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bye</lang> |
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{{out}} |
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<pre> |
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2 3 5 7 11 13 17 31 37 71 |
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73 79 97 101 107 113 131 149 151 157 |
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167 179 181 191 199 311 313 337 347 353 |
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359 373 383 389 |
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Count: 34 |
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</pre> |
</pre> |
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