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 is11(i.e.,2+3+5+1= 11).

Note:

Bonus point if you are able to do this using onlyO(n) extra space, where _n _is the total number of rows in the triangle.

• [x] #### adjacent element coordinate, line i, jth element is adjacent to level i+1, jth and (j+1)th element
• [x] #### the number of levels are equal to the total number in the last level
• [x] #### since it has the restriction of choosing the adjacent element in each level, so it means you could not just add up all the minimum numbers in each level
• [x] #### at first the res is [0,0,0,0,0] you use int[] res = new int[triangle.size() + 1] to initialize in case pointer out of boundary

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        if (triangle == null || triangle.size() == 0) {
            return 0;
        }
        int[] res = new int[triangle.size() + 1];
        int size = triangle.size();
        for (int i = size - 1; i >= 0;i--) {
            for (int j = 0; j < triangle.get(i).size(); j++) {
                res[j] = Math.min(res[j], res[j+1]) + triangle.get(i).get(j);
            }
        }
        return res[0];
    }
}