[LC] 339. Nested List Weight Sum

这题实在是简单的已经没法再解释啥了。最基本的图论题。想用bfs也行，用dfs也行, 只要在遍历的过程里记得自己是哪一层的即可。搞定，下面就给出dfs的代码：

class Solution {
    public int depthSum(List<NestedInteger> nestedList) {
        return depthSum(nestedList, 1);
    }
    
    public int depthSum(List<NestedInteger> nestedList, int depth) {
        int result = 0;
        for (NestedInteger ni : nestedList) {
            result += ni.isInteger() ? ni.getInteger() * depth : depthSum(ni.getList(), depth + 1);
        }
        
        return result;
    }
}

算了，活动了一下筋脉，再附送一个bfs的做法好了

    public int depthSum(List<NestedInteger> nestedList) {
        Queue<NestedInteger> nextLayer = new LinkedList<>();        
        Queue<NestedInteger> curLayer = new LinkedList<>();
        for (NestedInteger nInt : nestedList) {
            nextLayer.add(nInt);
        }

        int layer = 0;
        int result = 0;
        while(!nextLayer.isEmpty() || !curLayer.isEmpty()) {
            if (curLayer.isEmpty()) {
                Queue<NestedInteger> tmpLayer = curLayer;
                curLayer = nextLayer;
                nextLayer = tmpLayer;
                layer++;
            }
            
            NestedInteger nInt = curLayer.poll();
            if (nInt.isInteger()) {
                result += nInt.getInteger() * layer;
            } else {
                for (NestedInteger nextLayerElem : nInt.getList()) {
                    nextLayer.add(nextLayerElem);
                }
            }
        }
        
        return result;
    }