[java]最长连续整数序列，调试

Question

I have wrote a method for the question: input: an array of integers return: the length of longest consecutive integer sequence. like: for {9,1,2,3}, return 3, cuz{1,2,3}

the method doesnt run well. hope someone could help me with debugging.

public int solution(int[] arr){
    int counter = 1;
    int max = arr[1];
    //find the max in the array
    for (int i : arr){
        if (i > max){
            max  = i;
        }
    }

    int[] nArr = new int[max];
    for (int i : arr){
        nArr[i] = i;
    }

    List<Integer> counters = new ArrayList<>();
    for (int i = 0; i < max; i++){
        if (nArr[i] == nArr[i+1] - 1){
            counter++;
        }else{
            counters.add(counter);
            counter = 1;
        }
    }

    max = counters.get(1);
    for (int i : counters){
        if (i > max){
            max = i;
        }
    }
 return max;    }

thanks a lot!!!

Answer 1

You dont need to use ArrayList... If all you want is max count of sequential integers, then try this:

int[] a = somethingBlaBla;
int counter = 0; // Stores temporary maxes
int secCounter = 0; //Stores final max

for(int j = 0; j<a.length-1; j++){ // Iterate through array
    if(a[j] == a[j+1]-1){
        counter++; // If match found then increment counter
       if(counter > secCounter)
           secCounter = counter; // If current match is greater than stored match, replace current match
   }
    else
         counter = 0; // Reset match to accumulate new match
}
System.out.println(secCounter);

As for your method, the first thing I noticed is that max has value of greatest number in array and not the size of array. So if my array is something like {1,2,3,45,6,7,8,9} , it will throw indexOutOfBoundsException because its gonna try get 45th element in array which is not present.