120. 三角形最小路徑和

class Solution:
    def minimumTotal(self, triangle):
        """
        :type triangle: List[List[int]]
        :rtype: int
        """
        if not triangle:
            return
        ans = triangle[-1]
        for i in range(len(triangle)-2,-1,-1):
            for j in range(len(triangle[i])):
                ans[j] = min(ans[j],ans[j+1])+triangle[i][j]
        return ans[0]