Solve a few problems

03_revc/input.txt

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+AAAACCCGGT

03_revc/revc.nim

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+import os
+
+proc complement(c: char): char =
+    return case c:
+        of 'A': 'T'
+        of 'T': 'A'
+        of 'C': 'G'
+        of 'G': 'C'
+        else:
+            raise newException(ValueError, "Invalid letter")
+
+let fileName = paramStr(1)
+var dna = readFile(fileName)
+
+for i in 0 .. dna.len div 2:
+    let j = dna.len - 1 - i
+    if i > j:
+        break
+    elif i == j:
+        dna[i] = complement(dna[i])
+    else:
+        let temp = dna[i]
+        dna[i] = complement(dna[j])
+        dna[j] = complement(temp)
+
+echo dna
+
+

03_revc/rosalind_revc.txt

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+GCATCGGTCTTGGTACTGTCGGAACCGATATCTCTCGCCTTCGCTGAGTTGGTGGGCGTTGATACAGCCCAACATCCTCACACAGGAGCATTAAGTGACACCATGTGCGACGGCTGCCTCGCGAGCGAACGCCGCATTTCTCATAGTAGGGACTTGGTGATGGACATGATGTAGGCAGTGGGTCTGTCGCCGCCACCGCGCGCGTACTGGTCATTGACTAGGCTGTGTACTTAGGCATACAGCTTACGACTGACTGGACTTCCAATAACGTTATCGTTCTAGACTTGTTACGTAGGGAATGTACTTTGTTCGACTGACCTTCGTGACCCTGCTGTGCCCCGGGGACTACTACATTTGCTTTCACGCACGGTAGGGTTAACGTGATGGCTTGAAGGGGGCTCACCTCATAGGGATATGCTACACACCGACGAGGCATGACCATATGGGAGTCACACTGGCAAATTAAGGGCAGATCCGTCTCAATATGTCCCAAGTCAATGACTGGCGCCGACAGTGTCTCACGAAGATACACAGGGTCGAACATAGCAAGAGGTGAGAGGGCGGGGCAGCACTGTTAGGCCGCGCAATCCCGCTCGAGGATCACAGGAAGGGGCCCAACAGTAGTGACAGACAATCGGTTATGTCGGCCCTCCAACTGCGGCCTTACGAAAACTACAACTCCGATGAACGCACGGTCTACGGTCGTGTCTATGTGTATCTAACAGTTGTACATATTTCAGGAGTCAGACGCAGAACAACGGAAAAACAGCGCTCGAGACTTTGCCGCTAAGTAATCGCAGATCTTCAAATCGCTAGTCTGAATACACTAATCCGAAACTCTTGATGCACCTTGTTCTGCGTATCCGCTTTATCT