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NestedIterator.java
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NestedIterator.java
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package g0301_0400.s0341_flatten_nested_list_iterator;
// #Medium #Depth_First_Search #Tree #Stack #Design #Queue #Iterator #Programming_Skills_II_Day_18
// #2022_07_10_Time_2_ms_(99.95%)_Space_43.2_MB_(94.14%)
import com_github_leetcode.NestedInteger;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
/*
* // 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 empty list if this NestedInteger holds a single integer
* public List<NestedInteger> getList();
* }
*/
@SuppressWarnings("java:S2272")
public class NestedIterator implements Iterator<Integer> {
private Deque<ListIterator<NestedInteger>> stack;
private ListIterator<NestedInteger> it;
private NestedInteger next;
public NestedIterator(List<NestedInteger> nestedList) {
stack = new ArrayDeque<>();
it = nestedList.listIterator();
}
@Override
public Integer next() {
return next.getInteger();
}
@Override
public boolean hasNext() {
while (it.hasNext() || !stack.isEmpty()) {
// end of list
if (!it.hasNext()) {
it = stack.pop();
continue;
}
NestedInteger ni = it.next();
if (ni.isInteger()) {
next = ni;
return true;
} else {
stack.push(it);
it = ni.getList().listIterator();
}
}
return false;
}
}
/*
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i = new NestedIterator(nestedList);
* while (i.hasNext()) v[f()] = i.next();
*/