339. Nested List Weight Sum

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1:

Given the list [[1,1],2,[1,1]], return 10. (four 1''s at depth 2, one 2 at depth 1)

Example 2:

Given the list [1,[4,[6]]], return 27. (one 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27)

//recursive

public int depthSum(List<NestedInteger> nestedList) {

return helper(nestedList, 1);

}

public int helper(List<NestedInteger> nestedList, int depth){

if(nestedList==null||nestedList.size()==0)

return 0;

int sum=0;

for(NestedInteger ni: nestedList){

if(ni.isInteger()){

sum += ni.getInteger() * depth;

}else{

sum += helper(ni.getList(), depth+1);

}

}

return sum;

}

///////////////////////////////////////////////

//iterative

public int depthSum(List<NestedInteger> nestedList) {

int sum=0;

LinkedList<NestedInteger> queue = new LinkedList<NestedInteger>();

LinkedList<Integer> depth = new LinkedList<Integer>();

for(NestedInteger ni: nestedList){

queue.offer(ni);

depth.offer(1);

}

while(!queue.isEmpty()){

NestedInteger top = queue.poll();

int dep = depth.poll();

if(top.isInteger()){

sum += dep*top.getInteger();

}else{

for(NestedInteger ni: top.getList()){

queue.offer(ni);

depth.offer(dep+1);

}

}

}

return sum;

}