LeetCode : 341. Flatten Nested List Iterator

/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class NestedIterator implements Iterator<Integer> {

    Stack<NestedInteger> st;
    public NestedIterator(List<NestedInteger> nestedList) {
        st = new Stack();

        for (int i = nestedList.size()-1; i >= 0 ; i--)
            st.push(nestedList.get(i));
    }

    @Override
    public Integer next() {
        return st.pop().getInteger();        
    }

    @Override
    public boolean hasNext() {

        while(!st.isEmpty()) { // !!!
            NestedInteger top = st.peek();

            if(top.isInteger()) return true;

            st.pop(); // !!!
            for (int i = top.getList().size()-1; i >= 0; i--)
                st.push(top.getList().get(i));
        }

        return false;
    }
}

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i = new NestedIterator(nestedList);
 * while (i.hasNext()) v[f()] = i.next();
 */
congr / world

LeetCode : 341. Flatten Nested List Iterator #455
