README_EN.md

246. Strobogrammatic Number

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Description

Given a string num which represents an integer, return true if num is a strobogrammatic number.

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

 

Example 1:

Input: num = "69"
Output: true

Example 2:

Input: num = "88"
Output: true

Example 3:

Input: num = "962"
Output: false

Example 4:

Input: num = "1"
Output: true

 

Constraints:

• 1 <= num.length <= 50
• num consists of only digits.
• num does not contain any leading zeros except for zero itself.

Solutions

Python3

class Solution:
    def isStrobogrammatic(self, num: str) -> bool:
        def match(a, b):
            if a in {'0', '1', '8'}:
                return a == b
            if a == '6':
                return b == '9'
            if a == '9':
                return b == '6'
            return False
        n = len(num)
        i, j = 0, n - 1
        while i <= j:
            if not match(num[i], num[j]):
                return False
            i += 1
            j -= 1
        return True

Java

class Solution {
    public boolean isStrobogrammatic(String num) {
        int n = num.length();
        for (int i = 0, j = n - 1; i <= j; ++i, --j) {
            if (!match(num.charAt(i), num.charAt(j))) return false;
        }
        return true;
    }

    private boolean match(char a, char b) {
        switch (a) {
            case '0':
            case '1':
            case '8':
                return a == b;
            case '6':
                return b == '9';
            case '9':
                return b == '6';
            default:
                return false;
        }
    }
}

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