Description
You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.
Implement the NestedIterator class:
NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList.int next() Returns the next integer in the nested list.boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise.
Your code will be tested with the following pseudocode:
initialize iterator with nestedList
res = []
while iterator.hasNext()
append iterator.next() to the end of res
return res
If res matches the expected flattened list, then your code will be judged as correct.
Example 1:
Input: nestedList = [[1,1],2,[1,1]]
Output: [1,1,2,1,1]
Explanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].
Example 2:
Input: nestedList = [1,[4,[6]]]
Output: [1,4,6]
Explanation: By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,4,6].
Constraints:
1 <= nestedList.length <= 500- The values of the integers in the nested list is in the range
[-106, 106].
Solutions
Solution 1
PythonJavaC++GoTypeScriptRust
# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
# class NestedInteger:
# def isInteger(self) -> bool:
# """
# @return True if this NestedInteger holds a single integer, rather than a nested list.
# """
#
# def getInteger(self) -> int:
# """
# @return the single integer that this NestedInteger holds, if it holds a single integer
# Return None if this NestedInteger holds a nested list
# """
#
# def getList(self) -> [NestedInteger]:
# """
# @return the nested list that this NestedInteger holds, if it holds a nested list
# Return None if this NestedInteger holds a single integer
# """
class NestedIterator:
def __init__(self, nestedList: [NestedInteger]):
def dfs(ls):
for x in ls:
if x.isInteger():
self.nums.append(x.getInteger())
else:
dfs(x.getList())
self.nums = []
self.i = -1
dfs(nestedList)
def next(self) -> int:
self.i += 1
return self.nums[self.i]
def hasNext(self) -> bool:
return self.i + 1 < len(self.nums)
# Your NestedIterator object will be instantiated and called as such:
# i, v = NestedIterator(nestedList), []
# while i.hasNext(): v.append(i.next())(code-box)
/**
* // 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();
* }
*/
public class NestedIterator implements Iterator<Integer> {
private List<Integer> nums = new ArrayList<>();
private int i = -1;
public NestedIterator(List<NestedInteger> nestedList) {
dfs(nestedList);
}
@Override
public Integer next() {
return nums.get(++i);
}
@Override
public boolean hasNext() {
return i + 1 < nums.size();
}
private void dfs(List<NestedInteger> ls) {
for (var x : ls) {
if (x.isInteger()) {
nums.add(x.getInteger());
} else {
dfs(x.getList());
}
}
}
}
/**
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i = new NestedIterator(nestedList);
* while (i.hasNext()) v[f()] = i.next();
*/(code-box)
/**
* // 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) {
auto dfs = [&](this auto&& dfs, vector<NestedInteger>& ls) -> void {
for (auto& x : ls) {
if (x.isInteger()) {
nums.push_back(x.getInteger());
} else {
dfs(x.getList());
}
}
};
dfs(nestedList);
}
int next() {
return nums[++i];
}
bool hasNext() {
return i + 1 < nums.size();
}
private:
vector<int> nums;
int i = -1;
};
/**
* Your NestedIterator object will be instantiated and called as such:
* NestedIterator i(nestedList);
* while (i.hasNext()) cout << i.next();
*/(code-box)
/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* type NestedInteger struct {
* }
*
* // Return true if this NestedInteger holds a single integer, rather than a nested list.
* func (this NestedInteger) IsInteger() bool {}
*
* // 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
* // So before calling this method, you should have a check
* func (this NestedInteger) GetInteger() int {}
*
* // Set this NestedInteger to hold a single integer.
* func (n *NestedInteger) SetInteger(value int) {}
*
* // Set this NestedInteger to hold a nested list and adds a nested integer to it.
* func (this *NestedInteger) Add(elem NestedInteger) {}
*
* // Return the nested list that this NestedInteger holds, if it holds a nested list
* // The list length is zero if this NestedInteger holds a single integer
* // You can access NestedInteger's List element directly if you want to modify it
* func (this NestedInteger) GetList() []*NestedInteger {}
*/
type NestedIterator struct {
nums []int
i int
}
func Constructor(nestedList []*NestedInteger) *NestedIterator {
var dfs func([]*NestedInteger)
nums := []int{}
i := -1
dfs = func(ls []*NestedInteger) {
for _, x := range ls {
if x.IsInteger() {
nums = append(nums, x.GetInteger())
} else {
dfs(x.GetList())
}
}
}
dfs(nestedList)
return &NestedIterator{nums, i}
}
func (this *NestedIterator) Next() int {
this.i++
return this.nums[this.i]
}
func (this *NestedIterator) HasNext() bool {
return this.i+1 < len(this.nums)
}(code-box)
/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* class NestedInteger {
* If value is provided, then it holds a single integer
* Otherwise it holds an empty nested list
* constructor(value?: number) {
* ...
* };
*
* Return true if this NestedInteger holds a single integer, rather than a nested list.
* isInteger(): boolean {
* ...
* };
*
* Return the single integer that this NestedInteger holds, if it holds a single integer
* Return null if this NestedInteger holds a nested list
* getInteger(): number | null {
* ...
* };
*
* Set this NestedInteger to hold a single integer equal to value.
* setInteger(value: number) {
* ...
* };
*
* Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
* add(elem: NestedInteger) {
* ...
* };
*
* Return the nested list that this NestedInteger holds,
* or an empty list if this NestedInteger holds a single integer
* getList(): NestedInteger[] {
* ...
* };
* };
*/
class NestedIterator {
private nums: number[] = [];
private i = -1;
constructor(nestedList: NestedInteger[]) {
const dfs = (ls: NestedInteger[]) => {
for (const x of ls) {
if (x.isInteger()) {
this.nums.push(x.getInteger());
} else {
dfs(x.getList());
}
}
};
dfs(nestedList);
}
hasNext(): boolean {
return this.i + 1 < this.nums.length;
}
next(): number {
return this.nums[++this.i];
}
}
/**
* Your ParkingSystem object will be instantiated and called as such:
* var obj = new NestedIterator(nestedList)
* var a: number[] = []
* while (obj.hasNext()) a.push(obj.next());
*/(code-box)
// #[derive(Debug, PartialEq, Eq)]
// pub enum NestedInteger {
// Int(i32),
// List(Vec<NestedInteger>)
// }
struct NestedIterator {
nums: Vec<i32>,
i: usize,
}
/**
* `&self` means the method takes an immutable reference.
* If you need a mutable reference, change it to `&mut self` instead.
*/
impl NestedIterator {
fn new(nested_list: Vec<NestedInteger>) -> Self {
let mut nums = Vec::new();
Self::dfs(&nested_list, &mut nums);
NestedIterator { nums, i: 0 }
}
fn next(&mut self) -> i32 {
let result = self.nums[self.i];
self.i += 1;
result
}
fn has_next(&self) -> bool {
self.i < self.nums.len()
}
fn dfs(nested_list: &Vec<NestedInteger>, nums: &mut Vec<i32>) {
for ni in nested_list {
match ni {
NestedInteger::Int(x) => nums.push(*x),
NestedInteger::List(list) => Self::dfs(list, nums),
}
}
}
}(code-box)
