120. 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.

---

public class Solution {
public int minimumTotal(ArrayList<ArrayList<Integer>> triangle) {

int n = triangle.size();
int[] p = new int[n+1];

while(n > 0){
n--;
for(int i=0; i<=n; i++){
p[i] = triangle.get(n).get(i) + (p[i]<p[i+1] ? p[i] : p[i+1]);
}
}

return p[0];
}
}