[LeetCode] 339. Nested List Weight Sum_Easy tag:DFS-优快云博客

本文详细解析了一个深度加权求和算法，该算法针对一个嵌套整数列表，返回列表中所有整数的加权和，权重由其深度决定。通过深度优先搜索(DFS)策略，递归地遍历嵌套列表并计算每个元素的权重值。

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.

题目思路为DFS, 用一个helper function去记录nestInteger的值, 传入的input包括depth.

Data Structure.

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger(object):
#    def __init__(self, value=None):
#        """
#        If value is not specified, initializes an empty list.
#        Otherwise initializes a single integer equal to value.
#        """
#
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def add(self, elem):
#        """
#        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
#        :rtype void
#        """
#
#    def setInteger(self, value):
#        """
#        Set this NestedInteger to hold a single integer equal to value.
#        :rtype void
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """

Code

class Solution:
    def NestedListWeightSum(self, nestedList):
        def helper(nestedList, depth):
            s = 0
            for each in nestedList:
                if each.isInteger():
                    s += each.getInteger() * depth
                else:
                    s += dfs(each.getList(), depth + 1)
            return s
        return helper(nestedList, 1)