LeetCode341 展平巢狀列表迭代器
阿新 • • 發佈:2018-12-22
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:
Input: [[1,1],2,[1,1]]
Output: [1,1,2,1,1]
Explanation: By calling next repeatedly until hasNext returns false,
the order of elements returned by next should be: [1,1,2,1,1].
Example 2:
Input: [1,[4,[6]]]
Output: [1,4,6]
Explanation: By calling next repeatedly until hasNext returns false,
the order of elements returned by next should be: [1,4,6].
/** * // 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> stack = new Stack<>(); public NestedIterator(List<NestedInteger> nestedList) { for(int i = nestedList.size() - 1; i >= 0; i--){ stack.push(nestedList.get(i)); } } @Override public Integer next() { return stack.pop().getInteger(); } @Override public boolean hasNext() { while(!stack.isEmpty()){ NestedInteger curr = stack.peek(); if(curr.isInteger()) { return true; } stack.pop(); for(int i = curr.getList().size() - 1; i >= 0; i--) { stack.push(curr.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(); */