first commit

p19/solution.jl

@@ -0,0 +1,29 @@
+function solution()
+    n_months = 12
+    n_years = 100
+    n = 0
+    day = 1
+    for i = 1:n_months*n_years
+        if (day-1)%7+1 == 7
+            n += 1
+        end
+        day += step(i)
+    end
+    return n
+end
+
+function step(next::Int)
+    year = (next-1)÷12+1
+    month = (next-1)%12+1
+    if month ∈ [4, 6, 9, 11]
+        return 30
+    elseif month ∈ [1, 3, 5, 7, 8, 10, 12]
+        return 31
+    elseif year % 4 == 0
+        return 29
+    else return 28
+    end
+end
+
+# solved by chatGPT
+println(solution())