leetcode 120. Triangle

发表于 | 分类于

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

Note:

Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

1
2
3
4
5
6
7
8
9
10
11
12
13
class Solution(object):
    def minimumTotal(self, triangle):
        """
        :type triangle: List[List[int]]
        :rtype: int
        """
        #bottom-up
        #dp[i] = min(dp[i],dp[i+1]) + triangle[layer][i]
        dp = triangle[-1]
        for layer in xrange(len(triangle)-2,-1,-1):
            for i in xrange(len(triangle[layer])):
                dp[i] = min(dp[i],dp[i+1]) + triangle[layer][i]
        return dp[0]