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3208. Alternating Groups II

There is a circle of red and blue tiles. You are given an array of integers colors and an integer k. The color of tile i is represented by colors[i]:

  • colors[i] == 0 means that tile i is red.
  • colors[i] == 1 means that tile i is blue.

An alternating group is every k contiguous tiles in the circle with alternating colors (each tile in the group except the first and last one has a different color from its left and right tiles).

Return the number of alternating groups.

Note that since colors represents a circle, the first and the last tiles are considered to be next to each other.

Example 1:

Input: colors = [0,1,0,1,0], k = 3

Output: 3

Explanation:

img

Alternating groups:

imgimgimg

Example 2:

Input: colors = [0,1,0,0,1,0,1], k = 6

Output: 2

Explanation:

img

Alternating groups:

imgimg

Example 3:

Input: colors = [1,1,0,1], k = 4

Output: 0

Explanation:

img

Constraints:

  • 3 <= colors.length <= 105
  • 0 <= colors[i] <= 1
  • 3 <= k <= colors.length

Soluton:

class Solution {
    public int numberOfAlternatingGroups(int[] colors, int k) {

        int n = colors.length;

        // if(k<n) return 0;
        int answer=0;

        List<Integer> list = new ArrayList<>();
        for(int i:colors) list.add(i);
        for(int i=0;i<k-1;i++) list.add(colors[i]);
        // System.out.println(list);
        int start = 0;
        int end = 1;

        int len = 1;
        while(start<n && end<n+k-1){
            if(list.get(end)!=list.get(end-1)) {
                // end++;
                len++;
            }
            else{
                start = end;
                len =1;  
            }
            if(len==k){
                answer++;
                start++;
                len--;
            }
            end++;

        }

        return answer;


    }
}