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FlattenNestedListIterator.java
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FlattenNestedListIterator.java
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package com.algorithm.playground.leetcode.problems.lc300.lc340.lc341;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
/**
* https://leetcode.com/problems/flatten-nested-list-iterator/description/
*/
public class FlattenNestedListIterator {
public static NestedIterator nestedIterator(List<NestedInteger> list) {
return new FlattenNestedListIterator().createNestedIterator(list);
}
public static NestedInteger nestedInteger(Integer i) {
return new NestedIntegerImpl(i);
}
public static NestedInteger nestedInteger(List<NestedInteger> list) {
return new NestedIntegerImpl(list);
}
private NestedIterator createNestedIterator(List<NestedInteger> list) {
return new NestedIterator(list);
}
// 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.
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
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
List<NestedInteger> getList();
}
public static class NestedIntegerImpl implements NestedInteger {
private Integer i;
private List<NestedInteger> list;
NestedIntegerImpl(Integer i) {
this.i = i;
}
NestedIntegerImpl(List<NestedInteger> list) {
this.list = list;
}
// @return true if this NestedInteger holds a single integer, rather than a nested list.
@Override
public boolean isInteger() {
return i != null;
}
// @return the single integer that this NestedInteger holds, if it holds a single integer
// Return null if this NestedInteger holds a nested list
@Override
public Integer getInteger() {
return i;
}
// @return the nested list that this NestedInteger holds, if it holds a nested list
// Return null if this NestedInteger holds a single integer
@Override
public List<NestedInteger> getList() {
return list;
}
}
public class NestedIterator implements Iterator<Integer> {
private LinkedList<NestedInteger> stack = new LinkedList<>();
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()) {
if (stack.peek().isInteger()) {
return true;
}
NestedInteger ni = stack.pop();
List<NestedInteger> list = ni.getList();
if (list != null) {
for (int i = list.size() - 1; i >= 0; i--) {
stack.push(list.get(i));
}
}
}
return false;
}
}
}