Determine whether an integer is a palindrome. Do this without extra space.
Some hints:
Could negative integers be palindromes? (ie, -1)
If you are thinking of converting the integer to string, note the restriction of using extra space.
You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?
There is a more generic way of solving this problem.
#include <gtest/gtest.h> using namespace std; bool isPalindrome2(int x) { bool bResult = false; if (x < 0) { return false; } int tempData[20] = {0}; int tempIdx = 0; int tempX = x; long long rValue = 0; while (tempX) { tempData[tempIdx++] = tempX % 10; tempX /= 10; } for (int i=0; i<tempIdx;++i) { rValue = rValue*10 +tempData[i]; } return (x == rValue); } bool isPalindrome3(int x) { if (x < 0) return false; long long nValue = 0; int temp = x; while (temp) { nValue = nValue*10 + temp % 10; temp /= 10; } return (x == nValue); } bool isPalindrome(int x) { if (x < 0) return false; int dev = 1; while (x / dev >= 10) { dev *= 10; } while (x != 0) { int l = x / dev; int r = x % 10; if (l != r) return false; x = (x % dev) / 10; dev /= 100; } return true; } TEST(Pratices, tIsPalindrome) { // 123 false // 121 true // -111 false // 0 true // 2147483647 false ASSERT_FALSE(isPalindrome(123)); ASSERT_TRUE(isPalindrome(121)); ASSERT_FALSE(isPalindrome(-111)); ASSERT_TRUE(isPalindrome(0)); ASSERT_FALSE(isPalindrome(2147483647)); }
http://articles.leetcode.com/palindrome-number
原文：http://www.cnblogs.com/Quincy/p/5299279.html