【LeetCode】120. Triangle (3 solutions)

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.

使用bottom-up方法将最小值汇聚到root，将中间结果保存在开辟的空间curMin中。

class Solution {
public:
int minimumTotal(vector<vector<int> > &triangle) {
int m = triangle.size();
if(m == 0)
return 0;
else if(m == 1)
return triangle[0][0];

vector<int> curMin = triangle[m-1];
for(int i = m-2; i >= 0; i --)
{// for level i
for(int j = 0; j <= i; j ++)
{
curMin[j] = triangle[i][j] + min(curMin[j], curMin[j+1]);
}
}
return curMin[0];
}
};