Solve a few problems

05_fibd/fibd.nim

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+import os
+import std/strutils
+import sequtils
+
+let n = parseInt(paramStr(1))
+let m = parseInt(paramStr(2))
+
+# pairsByAge is a `seq` which contains the number of pairs
+# by their age.
+# So, element 0 is newborns, element 1 is 1-month-old pairs, etc.
+var pairsByAge = newSeq[int](m)
+pairsByAge[0] = 1
+
+for i in 1 ..< n:
+    # Calculates the new pairs at generation i.
+    # This is the sum of all adult pairs at previous generations,
+    # i.e., all elements of the `pairsByAge` array from 1 to m.
+    # This assumes k = 1.
+    var newPairs = pairsByAge[1..^1].foldl(a+b)
+
+    # Calculates the number of pairs for each age at this generation.
+    for j in countDown(m-1, 1):
+        pairsByAge[j] = pairsByAge[j-1]
+    
+    pairsByAge[0] = newPairs
+
+let total = pairsByAge.foldl(a+b)
+echo $total

05_fibd/rosalind_fibd.txt

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+85 20