leetcode-246. Strobogrammatic Number

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.

For example, the numbers “69”, “88”, and “818” are all strobogrammatic.
原题地址

首尾对比，只有五种匹配的方式：0-0, 1-1, 8-8, 6-9, 9-6。把这些存入hash table会方便许多。

bool isStrobogrammatic(string num) {
    int p_1 = 0;
    int p_2 = num.size() - 1;
    unordered_map<char, char> hash;
    hash['0'] = '0';
    hash['1'] = '1';
    hash['8'] = '8';
    hash['6'] = '9';
    hash['9'] = '6';
    while (p_2 >= p_1) {
        if (hash.count(num[p_1]) == 0 || hash[num[p_1]] != num[p_2]) {
            return false;
        }
        p_1++;
        p_2--;
    }
    return true;
}