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
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
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]
.一种说法认为不应该把给出的list转换并存在本地,应该直接在上面遍历
阅读:Java的Iterator class和ListIterator class
没什么可说的
/** * // 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 int index; private List<Integer> list; public NestedIterator(List<NestedInteger> nestedList) { list = getList(nestedList); index = 0; } private List<Integer> getList(List<NestedInteger> nestedList) { List<Integer> l = new ArrayList<>(); for (NestedInteger n : nestedList) { if (n.isInteger()) { l.add(n.getInteger()); }else { l.addAll(getList(n.getList())); } } return l; } @Override public Integer next() { int save = list.get(index); index++; return save; } @Override public boolean hasNext() { return index < list.size(); } } /** * Your NestedIterator object will be instantiated and called as such: * NestedIterator i = new NestedIterator(nestedList); * while (i.hasNext()) v[f()] = i.next(); */
Solution #2, 用stack
ToDo: https://leetcode.com/problems/flatten-nested-list-iterator/discuss/80147/Simple-Java-solution-using-a-stack-with-explanation
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