p341

LeetCode p341 Flatten Nested List Iterator 题解

1.题目：

Given a nested list of integers, implement an iterator to flatten it.

Each element is either an integer, or a list – whose elements may also be integers or other lists.

Example 1:
Given the list [[1,1],2,[1,1]],

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

Example 2:
Given the list [1,[4,[6]]],

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

题意：

实现一个数据结构

2.解题思路:

一层层脱壳，见代码。

3.代码

---

[title] [] [url] [link text]

 
/**
 * // 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> {

    private Stack<NestedInteger> stack = new Stack<NestedInteger>();


	public NestedIterator(List<NestedInteger> nestedList) {

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

	}

	@Override
	public Integer next() {

		return stack.pop().getInteger();

	}

	@Override
	public boolean hasNext() {

		while ( !stack.empty() && !stack.peek().isInteger()) {
			NestedInteger nestedInteger = stack.pop();
			List<NestedInteger> list = nestedInteger.getList();
			for (int i = list.size() - 1; i > -1; i--) {
				stack.push(list.get(i));
			}
		}
		return !stack.empty();

	}
   

}

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

---

4.一些总结：