[leetcode] problem 900 – rle iterator

Write an iterator that iterates through a run-length encoded sequence.

The iterator is initialized by RLEIterator(int[] A), where A is a run-length encoding of some sequence. More specifically, for all even i, A[i] tells us the number of times that the non-negative integer value A[i+1] is repeated in the sequence.

The iterator supports one function: next(int n), which exhausts the next n elements (n >= 1) and returns the last element exhausted in this way. If there is no element left to exhaust, next returns -1 instead.

For example, we start with A = [3,8,0,9,2,5], which is a run-length encoding of the sequence [8,8,8,5,5]. This is because the sequence can be read as “three eights, zero nines, two fives”.

Example

Input: [“RLEIterator”,”next”,”next”,”next”,”next”], [[[3,8,0,9,2,5]],[2],[1],[1],[2]]

Output: [null,8,8,5,-1]

Explanation:
RLEIterator is initialized with RLEIterator([3,8,0,9,2,5]).
This maps to the sequence [8,8,8,5,5].
RLEIterator.next is then called 4 times:

.next(2) exhausts 2 terms of the sequence, returning 8. The remaining sequence is now [8, 5, 5].

.next(1) exhausts 1 term of the sequence, returning 8. The remaining sequence is now [5, 5].

.next(1) exhausts 1 term of the sequence, returning 5. The remaining sequence is now [5].

.next(2) exhausts 2 terms, returning -1. This is because the first term exhausted was 5,
but the second term did not exist. Since the last term exhausted does not exist, we return -1.

Note

0 <= A.length <= 1000
A.length is an even integer.
0 <= A[i] <= 10^9
There are at most 1000 calls to RLEIterator.next(int n) per test case.
Each call to RLEIterator.next(int n) will have 1 <= n <= 10^9.

Code

private int curPos = 0;
private int[] A;

public (int[] A) {
    this.A = A;
}

public int next(int n) {
    while (curPos < A.length - 1 && n > A[curPos]) {
        n -= A[curPos];
        curPos += 2;
    }

    if (curPos > A.length - 1)
        return -1;

    A[curPos] -= n;
    return A[curPos + 1];
}

[leetcode] problem 900 – rle iterator

Example

Note

Code

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