Reduce allocations

src/Julia/Problems001-050/Problem004.jl

@@ -5,24 +5,33 @@ Created on 17 Jun 2021
 @email: daviddoji@pm.me
 
 Solution for Problem 4 of Project Euler
-https://projecteuler.net/problem=4
-=#
+https://projecteuler.net/problem=4 =#
+
+using BenchmarkTools
+using Profile
+
+function ispalindrome(n::Int64)
+    # return digits(n) == reverse!(digits(n))
+    for i in zip(digits(n), reverse!(digits(n)))
+        if i[1] ≠ i[end]
+            return false
+        end
+    end
+    return true
+end
 
 function Problem4()
     #= 
     A palindromic number reads the same both ways. The largest palindrome made
     from the product of two 2-digit numbers is 9009 = 91 x 99.
 
-    Find the largest palindrome made from the product of two 3-digit numbers.
-    =#
-    ans = 0
-    for i in 100:1000
-        for j in 100:1000
-            palindrome = i * j
-            s = string(palindrome)
-            if (s==reverse(s)) & (palindrome > ans)
-                ans = palindrome
-            end
+    Find the largest palindrome made from the product of two 3-digit numbers. =#
+
+    ans = 10_001
+    for i in 100:999, j in i:999
+        num = i * j
+        if (num > ans) && ispalindrome(num)
+            ans = num
         end
     end
 
@@ -31,6 +40,6 @@ end
 
 
 println("Time to evaluate Problem 4:")
-@time Problem4()
+@btime Problem4()
 println("")
 println("Result for Problem 4: ", Problem4())