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 + 42 + 63 = 27)
這道題要用草稿紙拿例子演示幾次，才能發(fā)現(xiàn)level應(yīng)該在遍歷到整數(shù)的時(shí)候乘锈候，而在遍歷到list的時(shí)候不乘。并且在遍歷到list的時(shí)候，調(diào)用遞歸函數(shù)要記得level + 1.
/**
* // 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 null if this NestedInteger holds a single integer
* public List<NestedInteger> getList();
* }
*/
public class Solution {
public int depthSum(List<NestedInteger> nestedList) {
return helper(nestedList, 1);
}
private int helper(List<NestedInteger> nestedList, int level){
int sum = 0;
for (int i = 0; i < nestedList.size(); i++){
if (nestedList.get(i).isInteger()){
sum += level * nestedList.get(i).getInteger();
} else {
List<NestedInteger> list = nestedList.get(i).getList();
sum += helper(list, level + 1);
}
}
return sum;
}
}
