题目来源
https://leetcode.com/problems/triangle/
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.
题意分析
Input:一个三角矩阵
Output:最短路径
Conditions:使用O(n)空间
题目思路
首先初始化一个n大小的array，然后，初始化array为0，array[0]就是triangle的第一行的值，然后遍历剩余行，不断更新array，注意要从后往前遍历，否则会覆盖前面值。
AC代码（Python）
class Solution(object):
def minimumTotal(self, triangle):
"""
:type triangle: List[List[int]]
:rtype: int
"""
if len(triangle) == 0: return 0
array = [0 for i in range(len(triangle))]
array[0] = triangle[0][0]
for i in range(1,len(triangle)):
for j in range(len(triangle[i]) - 1, -1, -1):
if j == len(triangle[i]) - 1:
array[j] = array[j - 1] + triangle[i][j]
elif j == 0:
array[j] = array[j] + + triangle[i][j]
else:
array[j] = min(array[j-1], array[j]) + triangle[i][j]
return min(array)