9. Palindrome Number

發表於 | 分類於

problem

solution

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class Solution {
public:
    bool isPalindrome(int x) {
        // 0, 1,2,3,4,5,6,7,8,9 => true
        // 10 , 100, x0, x00 => false
        if (x < 0 || (x % 10 == 0 && x != 0)) return false;
        int ret = 0;
        while(ret < x){
            ret = 10*ret + (x%10);
            x/=10;
        }
        return ( ret==x || ret/10 == x);
    }
};

analysis

  • time complexity O(logn)
  • space complexity O(1)