Zigzag Iterator 540

Question

Given two 1d vectors, implement an iterator to return their elements alternately.

Example

Given two 1d vectors:

v1 = [1, 2]

v2 = [3, 4, 5, 6]

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1, 3, 2, 4, 5, 6].

Solution

这道题可以直接调用list的iterator来实现，只要用一个计数来确定应该用哪个iteraor即可。当然也可以自己用两个index来实现，但是iterator在内存中占用空间更小，并且更方便操作。

代码如下：

public class ZigzagIterator {
    /**
     * @param v1 v2 two 1d vectors
     */
    //用iterator更省空间
    Iterator<Integer> it1;
    Iterator<Integer> it2;
    int count;
    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        // initialize your data structure here.
        it1 = v1.iterator();
        it2 = v2.iterator();
        count = 0;
    }

    public int next() {
        // Write your code here
        count++;
        if((count % 2 == 1 && it1.hasNext()) || !it2.hasNext()){
            return it1.next();
        }else if((count % 2 == 0 && it2.hasNext()) || !it1.hasNext()){
            return it2.next();
        }
        return -1;
    }

    public boolean hasNext() {
        // Write your code here
        return it1.hasNext() || it2.hasNext();
    }
}

/**
 * Your ZigzagIterator object will be instantiated and called as such:
 * ZigzagIterator solution = new ZigzagIterator(v1, v2);
 * while (solution.hasNext()) result.add(solution.next());
 * Output result
 */