A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Write a function to determine if a number is strobogrammatic. The number is represented as a string.

Example 1:

Input:  "69"Output: true

Example 2:

Input:  "88"Output: true

Example 3:

Input:  "962"Output: false

 

把符合条件的数字(0,1,6,8,9)放进HashMap，双指针分别从0, length-1位置向中间扫描字符串

time: O(n), space: O(1)

class Solution {    public boolean isStrobogrammatic(String num) {        Map
     
       map = new HashMap<>();        map.put('0', '0');        map.put('1', '1');        map.put('6', '9');        map.put('8', '8');        map.put('9', '6');                int i = 0, j = num.length() - 1;        while(i <= j) {            char s = num.charAt(i), t = num.charAt(j);            if(s != t && !map.containsKey(s) || !map.containsKey(t) || map.get(s) != t)                return false;            i++;            j--;        }        return true;    }}