[leetcode]339. Nested List Weight Sum嵌套列表加权和

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:

Input: [[1,1],2,[1,1]]
Output: 10 
Explanation: Four 1's at depth 2, one 2 at depth 1.

Example 2:

Input: [1,[4,[6]]]
Output: 27 
Explanation: One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27.

题意：

嵌套列表加权和

Solution1： BFS(level order traversal) 是最快的

code

class Solution {
   public int depthSum(List<NestedInteger> nestedList) {
       // corner case 
        if(nestedList == null){return 0;} 
       // initialize
        int result = 0;
        int depth = 1;
       // put each item of list into the queue
        Queue<NestedInteger> queue = new LinkedList<>(nestedList);
        while(!queue.isEmpty()){
            // depends on different depth, queue size is changeable 
            int size = queue.size();  
            for(int i = 0; i < size; i++){
                NestedInteger n = queue.poll();
                if(n.isInteger()){
                    result += n.getInteger() * depth;
                }else{
                    // put each item of list into the queue
                    queue.addAll(n.getList());
                }
            }
            depth++;
        } 
    return result;
    }
}

注意：   put each item of list into the queue 的写法有：

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

for（NestedInteger n :nestedList）{
　　　　queue.add(n)
}

queue.addAll(nestedList)

Solution2: DFS

code

class Solution {
    public int depthSum(List<NestedInteger> nestedList) {
        if(nestedList == null) return 0;
        return dfs(nestedList, 1);    
    }
    
    private int dfs(List<NestedInteger> nestedList, int depth){
        int result = 0;
        for(NestedInteger n : nestedList ){
            if(n.isInteger()){
                result = result + n.getInteger()*depth;
            }else{
                result = result + dfs(n.getList() , depth+1);
            }  
        }
        return result ;
    }
}