CODEWITHSUNDEEP
javaalgorithmvector
Klausos Klausos
Klausos Klausos

Reputation: 16050

Get vector index positions of based on a condition

Let's say I have the vector vals and a number n:

boolean[] vals = new boolean[]{false, true, true, false, false, 
                               true, false, true, true};

int n = 2;

I need to define if the vector vals has n sequential nodes equal to true. If it has, then I want to get index positions of these nodes. For instance, in the above-given example, the answer is:

{{1,2},{7,8}}

Upvotes: 2

Views: 138

Answers (1)

aioobe
aioobe

Reputation: 421040

Here's one approach.

public static int[][] subSeqs(boolean[] vals, int n) {
    List<int[]> result = new ArrayList<>();
    int i = -1;
    for (int j = 0; j <= vals.length; j++) {
        boolean b = j == vals.length ? false : vals[j];
        if (b && i == -1) {          // going from false to true
            i = j;
        } else if (!b && i != -1) {  // going from true to false
            if (j-i >= n)
                result.add(new int[] { i, j-1 });
            i = -1;
        }
    }
    return result.toArray(new int[result.size()][]);
}

Basically i is a "state" variable updated during iteration over the array.

  • When i is -1, we're in a false sequence
  • When i is a non-negative number it represents the index of the first true, in the current true sequence.

So, when we switch from false to true we set i to the current index, and when we switch from true to false we check if the just-finished true sequence was >= n.

Upvotes: 2

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