Flatten Nested List Iterator问题及解法

问题描述：

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.

示例:

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]

.

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]

.
问题分析：

将nestedlist中的值倒序存在stack中，对stack的首元素进行分析，若为整数，则可以输出，若还是nestedlist，重复前面的操作。

过程详见代码：

class NestedIterator {
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blic:

stack<NestedInteger> s;
NestedIterator(vector<NestedInteger>& nestedList) {
for (int i = nestedList.size() - 1; i >= 0; i--)
{
s.push(nestedList[i]);
}
}

int next() {
int res = s.top().getInteger();
s.pop();
return res;
}

bool hasNext() {
while (!s.empty())
{
NestedInteger t = s.top();
if (t.isInteger()) return true;
s.pop();
vector<NestedInteger>& adjs = t.getList();
for (int i = adjs.size() - 1; i >= 0; i--)
{
s.push(adjs[i]);
}
}
return false;
}
};