# 341. Flatten Nested List Iterator 扁平化嵌套列表迭代器

@TOC

## # 题目描述

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].

## # 解题方法

### # 递归+队列

Python代码如下：

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger(object):
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """

class NestedIterator(object):

def __init__(self, nestedList):
"""
:type nestedList: List[NestedInteger]
"""
self.queue = collections.deque()
def getAll(nests):
for nest in nests:
if nest.isInteger():
self.queue.append(nest.getInteger())
else:
getAll(nest.getList())
getAll(nestedList)

def next(self):
"""
:rtype: int
"""
return self.queue.popleft()

def hasNext(self):
"""
:rtype: bool
"""
return len(self.queue)

# Your NestedIterator object will be instantiated and called as such:
# i, v = NestedIterator(nestedList), []
# while i.hasNext(): v.append(i.next())

### # 栈

C++代码如下：

/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* class NestedInteger {
*   public:
*     // Return true if this NestedInteger holds a single integer, rather than a nested list.
*     bool isInteger() const;
*
*     // Return the single integer that this NestedInteger holds, if it holds a single integer
*     // The result is undefined if this NestedInteger holds a nested list
*     int getInteger() const;
*
*     // Return the nested list that this NestedInteger holds, if it holds a nested list
*     // The result is undefined if this NestedInteger holds a single integer
*     const vector<NestedInteger> &getList() const;
* };
*/
class NestedIterator {
public:
NestedIterator(vector<NestedInteger> &nestedList) {
for (int i = nestedList.size() - 1; i >= 0; --i) {
st.push(nestedList[i]);
}
}

int next() {
NestedInteger cur = st.top(); st.pop();
return cur.getInteger();
}

bool hasNext() {
while (!st.empty()) {
NestedInteger cur = st.top();
if (cur.isInteger()) {
return true;
}
st.pop();
for (int i = cur.getList().size() - 1; i >= 0; --i) {
st.push(cur.getList()[i]);
}
}
return false;
}
private:
stack<NestedInteger> st;
};

/**
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i(nestedList);
* while (i.hasNext()) cout << i.next();
*/

## # 日期

2018 年 3 月 12 日 2019 年 10 月 2 日 —— 欢度国庆