120. 三角形最小路径和

https://leetcode-cn.com/problems/triangle/submissions/
dp,自底向上

class Solution:
    def minimumTotal(self, triangle):
        """
        :type triangle: List[List[int]]
        :rtype: int
        """
        n = len(triangle)
        dp = [triangle[-1]] * n  #初始矩阵为最后一行*n

        for i in range(n-2, -1, -1):
            size = len(triangle[i])
            for j in range(size):
                dp[i][j] = min(dp[i][j], dp[i][j+1]) + triangle[i][j]
        return dp[0][0]

优化：每次迭代后该行不再使用，可以覆盖，只用一个list做dp

class Solution:
    def minimumTotal(self, triangle):
        """
        :type triangle: List[List[int]]
        :rtype: int
        """
        n = len(triangle)
        dp = triangle[-1]
        
        for i in range(n-2, -1, -1):
            size = len(triangle[i])
            for j in range(size):
                dp[j] = min(dp[j], dp[j+1]) + triangle[i][j]
        return dp[0]