Largest palindrome product: Difference between revisions

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 =={{header|Ring}}==
-<lang ring>
+<lang ring>? "working..."
-load "stdlib.ring"
-see "working..." + nl
-prodOld = 0
+prod = 1
+bestProd = 0
-limitStart = 100
+// maximum 3 digit number
-limitEnd = 999
+max = 999
+// both factors must be >100 for a 6 digit product
+limitStart = 101
+// one factor must be divisible by 11
+limitEnd = 11 * floor(max / 11)
+second = limitStart
+iters = 0
+// loop from hi to low to find the best result in the fewest steps
-for n = limitStart to limitEnd
-    for m = limitStart to limitEnd
+for n = limitEnd to limitStart step -11
+    // with n falling, the lower limit of m can rise with
-        prodNew = n*m
+    // the best-found-so-far second number. Doing this
-        if prodNew > prodOld and palindrome(string(prodNew))
+    // lowers the iteration count by a lot.
-           prodOld = prodNew
-           first = n
+    for m = max to second step -1
-           second = m
+        prod = n * m
+        if isPal(prod)
+            iters++
+            // exit when the product stops increasing
+            if bestProd > prod
+                exit
+            ok
+            // maintain the best-found-so-far result
+            first = n
+            second = m
+            bestProd = prod
         ok
     next
 next
-see "The largest palindrome is:" + nl
+put "The largest palindrome is: "
-see "" + first + " * " + second + " = " + prodOld + nl
+? "" + bestProd + " = " + first + " * " + second
+? "Found in " + iters + " iterations"
-see "done..." + nl
+put "done..."
-</lang>
+func isPal n
+    x = string(n)
+    l = len(x) + 1
+    i = 0
+    while i < l
+        if x[i++] != x[l--]
+            return false
+        ok
+    end
+    return true</lang>
 {{out}}
-<pre>
+<pre>working...
+The largest palindrome is: 906609 = 913 * 993
-working...
+Found in 6 iterations
-The largest palindrome is:
+done...</pre>
-* 993 = 906609
-done...
-</pre>
 =={{header|Wren}}==