2103-rings-and-rods.js

/**
 * 2103. Rings and Rods
 * https://leetcode.com/problems/rings-and-rods/
 * Difficulty: Easy
 *
 * There are n rings and each ring is either red, green, or blue. The rings are distributed across
 * ten rods labeled from 0 to 9.
 *
 * You are given a string rings of length 2n that describes the n rings that are placed onto the
 * rods. Every two characters in rings forms a color-position pair that is used to describe each
 * ring where:
 * - The first character of the ith pair denotes the ith ring's color ('R', 'G', 'B').
 * - The second character of the ith pair denotes the rod that the ith ring is placed on
 *   ('0' to '9').
 *
 * For example, "R3G2B1" describes n == 3 rings: a red ring placed onto the rod labeled 3, a green
 * ring placed onto the rod labeled 2, and a blue ring placed onto the rod labeled 1.
 *
 * Return the number of rods that have all three colors of rings on them.
 */

/**
 * @param {string} rings
 * @return {number}
 */
var countPoints = function(rings) {
  const map = new Map();

  for (let i = 0; i < rings.length; i += 2) {
    const color = rings[i];
    const rod = rings[i + 1];
    if (!map.has(rod)) map.set(rod, new Set());
    map.get(rod).add(color);
  }

  let result = 0;
  for (const colors of map.values()) {
    if (colors.size === 3) result++;
  }

  return result;
};