Problem
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 listnestedList
.int next()
Returns the next integer in the nested list.boolean hasNext()
Returnstrue
if there are still some integers in the nested list andfalse
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
[-10^6, 10^6]
.
Solution (Java)
/**
* // 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 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();
*/
Solution (Javascript)
/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* function NestedInteger() {
*
* Return true if this NestedInteger holds a single integer, rather than a nested list.
* @return {boolean}
* this.isInteger = function() {
* ...
* };
*
* Return the single integer that this NestedInteger holds, if it holds a single integer
* Return null if this NestedInteger holds a nested list
* @return {integer}
* this.getInteger = function() {
* ...
* };
*
* Return the nested list that this NestedInteger holds, if it holds a nested list
* Return null if this NestedInteger holds a single integer
* @return {NestedInteger[]}
* this.getList = function() {
* ...
* };
* };
*/
/**
* @constructor
* @param {NestedInteger[]} nestedList
*/
var NestedIterator = function(nestedList) {
this.data = []
this.flatten(nestedList)
};
/**
* @this NestedIterator
* @returns {boolean}
*/
NestedIterator.prototype.hasNext = function() {
return this.data.length
};
/**
* @this NestedIterator
* @returns {integer}
*/
NestedIterator.prototype.next = function() {
return this.data.shift()
};
/**
* Your NestedIterator will be called like this:
* var i = new NestedIterator(nestedList), a = [];
* while (i.hasNext()) a.push(i.next());
*/
NestedIterator.prototype.flatten = function(list) {
for (let el of list)
if (el.isInteger()) this.data.push(el.getInteger())
else this.flatten(el.getList())
};
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).