Question:

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"
  2. Output: [[3,6]]
  3. Explanation: "xxxx" is the single large group with starting  3 and ending positions 6.
  1. Input: "abc"
  2. Output: []
  3. Explanation: We have "a","b" and "c" but no large group.
  6. Input: "abcdddeeeeaabbbcd"
  7. Output: [[3,5],[6,9],[12,14]]

Solution:

  1. /**
  2.  * @param {string} S
  3.  * @return {number[][]}
  4.  */
  5. var largeGroupPositions = function(S) {
  6.     let result = [];
  7.     let arr = S.split('');
  8.     let curIndex = 0;
  9.     let curItem = arr[0];
  10.     let j = 1 ;
  11.     for (let i = 1; i< arr.length ; i ++ ){
  12.         if(arr[i]!=curItem){
  13.             if(j >= 3) {
  14.               result.push([curIndex, i-1])
  15.             }
  16.             curItem = arr[i];
  17.             curIndex = i;
  18.             j = 1;
  19.         }else{
  20.             j ++ ;
  21.             if(i===arr.length-1 && j >=3){
  22.               result.push([curIndex, i])
  23.             }
  25.         }
  26.     }
  27.     return result;
  28. };