positions-of-large-groups.js

/**
 * Positions of Large Groups
 *
 * In a string S of lowercase letters, these letters form consecutive groups of the same character.
 *
 * For example, a string like S = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z" and "yy".
 *
 * Call a group large if it has 3 or more characters.  We would like the starting and ending positions of every large group.
 *
 * The final answer should be in lexicographic order.
 *
 * Example 1:
 *
 * Input: "abbxxxxzzy"
 * Output: [[3,6]]
 * Explanation: "xxxx" is the single large group with starting  3 and ending positions 6.
 *
 * Example 2:
 *
 * Input: "abc"
 * Output: []
 * Explanation: We have "a","b" and "c" but no large group.
 *
 * Example 3:
 *
 * Input: "abcdddeeeeaabbbcd"
 * Output: [[3,5],[6,9],[12,14]]
 *
 * Note:  1 <= S.length <= 1000
 */

/**
 * @param {string} S
 * @return {number[][]}
 */
const largeGroupPositions = S => {
  const result = [];

  let i = 0;
  let j = 0;

  while (j < S.length) {
    while (j < S.length && S[i] === S[j]) {
      j++;
    }

    const len = j - i;

    if (len >= 3) {
      result.push([i, j - 1]);
    }

    i = j;
  }

  return result;
};

export { largeGroupPositions };