Raghav Raghav - 3 months ago 7
Java Question

Test Cases fail to satisfy

I'm just a beginner. I came across this question for which my code fails to satisfy all/most of the test cases.

Question:


Given an array of numbers, find the number of non-empty sub-arrays in which the minimum and maximum element are identical.


Example:


Input: Array = [1, 1, 3]

Output: 4


Explanation:


The required sub-arrays are [1], [1], [3], [1,1]


My solution:


Sort the array and solve the problem.


Code:

for(int i = 0; i < testCases; i++){
int arraySize = in.nextInt();
int array[] = new int[arraySize];
for(int j = 0; j < arraySize; j++){
array[j] = in.nextInt();
}
temp[i] = (findSubArrays(array));
}
for(int i = 0; i < testCases; i++){
System.out.println(temp[i]);
}

private static int findSubArrays(int[] array) {
Arrays.sort(array);

//Since each element can form a sub-array of its own
int noOfSubArrays = array.length;

for(int i = 0; i < array.length-1; i++){
if(array[i] == array[i+1]){
noOfSubArrays++;
}
}
return noOfSubArrays;
}

Answer

So you're sorting the array to keep begin points and end points adjacent so you don't need a nested traversal. That makes sense. The problem is that you're counting adjacent duplicates, but what you really need is T(n), or the triangle number of consecutive duplicates. Consider a simple scenario:

[1, 1, 1]

Your algorithm returns 5, but there are actually 6 subsets (by start & end index):

0, 0
0, 1
0, 2
1, 1
1, 2
2, 2

So let's update the algorithm to calculate the triangle number of each sequence:

private static int findSubArrays(int... array) {
    Arrays.sort(array);

    int sequenceCount = 0;
    int total = 0;
    for (int i = 0; i < array.length + 1; i++) {
        if (i == array.length || (i > 0 && array[i] != array[i - 1])) {
            total += triangle(sequenceCount);
            sequenceCount = 0;
        }
        sequenceCount++;
    }
    return total;
}

private static int triangle(int n) {
    return (n * (n + 1)) / 2;
}

Now calling findSubArrays(1, 1, 1) returns 6 and findSubArrays(1, 1, 3) returns 4.

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