0246. Strobogrammatic Number.js

// 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

/**
 * @param {string} num
 * @return {boolean}
 */

// Two pointers
// Time O(n)
// Space O(1)
const isStrobogrammatic = (num) => {
  const map = {
    '0': '0',
    '1': '1',
    '6': '9',
    '9': '6',
    '8': '8',
  };

  let l = 0;
  let r = num.length - 1;
  while (l <= r) {
    if (num[r] !== map[num[l]]) return false;
    l++;
    r--;
  }
  return true;
};