EPI: is number palindromic (CPP/Py)

Author: jsgoller1

elements-of-programming-interviews/cpp/is_number_palindromic.cc

@@ -1,7 +1,18 @@
 #include "test_framework/generic_test.h"
 bool IsPalindromeNumber(int x) {
-  // TODO - you fill in here.
-  return true;
+  if (x < 0) {
+    return false;
+  }
+
+  int original = x;
+  int revX = 0;
+  while (x) {
+    revX *= 10;
+    revX += x % 10;
+    x /= 10;
+  }
+
+  return original == revX;
 }
 
 int main(int argc, char* argv[]) {

elements-of-programming-interviews/problem_mapping.js

@@ -128,15 +128,15 @@ problem_mapping = {
         },
         "4.09 Check if a decimal integer is a palindrome": {
             "C++: is_number_palindromic.cc": {
-                "passed": 0,
+                "passed": 20000,
                 "total": 20000
             },
             "Java: IsNumberPalindromic.java": {
                 "passed": 0,
                 "total": 20000
             },
             "Python: is_number_palindromic.py": {
-                "passed": 0,
+                "passed": 20000,
                 "total": 20000
             }
         },

elements-of-programming-interviews/python/is_number_palindromic.py

@@ -1,9 +1,30 @@
 from test_framework import generic_test
 
 
+# Palindrome reads forward and backward the same way,
+# so just reverse and compare; can do this a few ways.
+
+def is_palindrome_number_simple(x: int) -> bool:
+    if x < 0:
+        return False
+    return str(x)[::-1] == str(x)
+
+
 def is_palindrome_number(x: int) -> bool:
-    # TODO - you fill in here.
-    return True
+    """
+    If the interviewer says "no conversion to string",
+    then just compute the reversed decimal value and
+    compare to the original.
+    """
+    if x < 0:
+        return False
+    original = x
+    rev_x = 0
+    while (x):
+        rev_x *= 10
+        rev_x += x % 10
+        x = x//10
+    return original == rev_x
 
 
 if __name__ == '__main__':