/** * // 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(); * } */ publicclassNestedIteratorimplementsIterator<Integer> { Stack<NestedInteger> stack = new Stack<>(); publicNestedIterator(List<NestedInteger> nestedList){ for (int i = nestedList.size() - 1; i >= 0; i--) { stack.push(nestedList.get(i)); } }
@Override public Integer next(){ hasNext(); return stack.pop().getInteger(); }
@Override publicbooleanhasNext(){ while (!stack.isEmpty()) { NestedInteger cur = stack.peek(); if (cur.isInteger()) { returntrue; } stack.pop(); for (int i = cur.getList().size() - 1; i >= 0; i--) { stack.push(cur.getList().get(i)); } } returnfalse; } }
/** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i = new NestedIterator(nestedList); * while (i.hasNext()) v[f()] = i.next(); */