[leetcode] 339. Nested List Weight Sum @ python

最新推荐文章于 2020-05-21 08:50:01 发布

原创最新推荐文章于 2020-05-21 08:50:01 发布 · 934 阅读

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本文介绍了一种针对嵌套整数列表的深度加权求和算法，通过BFS遍历方式，计算列表中所有整数与其深度的乘积之和。示例包括[[1,1],2,[1,1]]和[1,[4,[6]]]的求和过程及结果。

原题

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 + 42 + 63 = 27.
Accepted
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Submissions
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解法

BFS. 初始化depth和ans, 遍历nestedList, 每次遍历将加权的和累加至ans里, 然后递增depth.
Time: O(n), n是nestList的数字个数.
Space: O(n)

代码

# """
# 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]
#        """

class Solution(object):
    def depthSum(self, nestedList):
        """
        :type nestedList: List[NestedInteger]
        :rtype: int
        """
        depth, ans = 1, 0
        while nestedList:
            ans += depth*sum([i.getInteger() for i in nestedList if i.isInteger()])
            newList = []
            for i in nestedList:
                if not i.isInteger():
                    newList += i.getList()
            nestedList = newList            
            depth += 1
        return ans