codility.js

function solution(A) {
  if (A.length === 1) return 0;

  var len = A.length, result = 0, revers = 0;
  
  for(var l = 0; l < len; l++) {
    var count = 0;
    
    if (l > 0) {
      count = (A[l-1] !== A[l]) ? count + 1 : count - 1 ;
    }
    
    if (l < len-1) {
      if (A[l] !== A[l+1]) {
        count++;
      } else {
        count--;
        // how many pairs of coins we have now 
        result++;
      }      
    }   
    revers = Math.max(revers, count);
  }
  return result + revers;
}
console.log(solution([ 1, 1, 0, 1, 0, 0, 1, 1 ])); // 5
console.log(solution([ 1, 1, 1, 1, 1, 0, 1, 1 ])); // 7
console.log(solution([ 1, 1, 1, 1, 1])); // 4
console.log(solution([ 1, 0, 1])); // 2
console.log(solution([ 1, 1, 1, 0])); // 2
console.log(solution([ 1, 1, 0, 0, 0])); // 3