Java DFS


  • 0
    /**
     * // 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<Iterator<NestedInteger>> stack = new Stack<Iterator<NestedInteger>>();
        Integer nextInteger;
        public NestedIterator(List<NestedInteger> nestedList) {
            stack.push(nestedList.iterator());
        }
    
        @Override
        public Integer next() {
            return nextInteger;
        }
    
        @Override
        public boolean hasNext() {
            //DFS to find a integer
            while (!stack.empty()) {
                if(stack.peek().hasNext()){
                    NestedInteger ni = stack.peek().next();
                    if(ni.isInteger()){
                        nextInteger = ni.getInteger();
                        return true;
                    } else {
                        stack.push(ni.getList().iterator());
                    }
                } else {
                    stack.pop();
                }
            }
            return false;
        }
    }
    
    /**
     * Your NestedIterator object will be instantiated and called as such:
     * NestedIterator i = new NestedIterator(nestedList);
     * while (i.hasNext()) v[f()] = i.next();
     */
    

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