364. Nested List Weight Sum II

I made a mistake in first place where I was trying to get the maximum level for each nested list. This will get sum -2 for case [[-1], [[-1]]], which is wrong. We actually only need to get the maximum level once and pass the maximum level decreasingly down along the nested list.

1:  /**  
2:   * // This is the interface that allows for creating nested lists.  
3:   * // You should not implement it, or speculate about its implementation  
4:   * class NestedInteger {  
5:   *  public:  
6:   *   // Return true if this NestedInteger holds a single integer, rather than a nested list.  
7:   *   bool isInteger() const;  
8:   *  
9:   *   // Return the single integer that this NestedInteger holds, if it holds a single integer  
10:   *   // The result is undefined if this NestedInteger holds a nested list  
11:   *   int getInteger() const;  
12:   *  
13:   *   // Return the nested list that this NestedInteger holds, if it holds a nested list  
14:   *   // The result is undefined if this NestedInteger holds a single integer  
15:   *   const vector<NestedInteger> &getList() const;  
16:   * };  
17:   */  
18:  class Solution {  
19:  private:  
20:    int max_depth = 0;  
21:  public:  
22:    int depthSumInverse(vector<NestedInteger>& nestedList) {  
23:      depth(nestedList, 1);  
24:      return helper(nestedList, max_depth);  
25:    }  
26:    void depth(vector<NestedInteger> &nestedList, int d) {  
27:      max_depth = max(d, max_depth);  
28:      for (int i = 0; i < nestedList.size(); i++) {  
29:        if (!nestedList[i].isInteger()) depth(nestedList[i].getList(), d+1);  
30:      }  
31:    }  
32:    int helper(vector<NestedInteger> &nestedList, int d) {  
33:      int sum = 0;  
34:      for (int i = 0; i < nestedList.size(); i++) {  
35:        if (nestedList[i].isInteger()) sum += d * nestedList[i].getInteger();  
36:        else sum += helper(nestedList[i].getList(), d-1);  
37:      }  
38:      return sum;  
39:    }  
40:  };