【LeetCode】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) {

        if(triangle.size()==0)

            return 0;

        int len = triangle.size();

        int[] re = new int[len];

        re[0]=triangle.get(0).get(0);

        int min=re[0];

        for(int i=1;i<triangle.size();i++){

            ArrayList<Integer> al = triangle.get(i);

            int pre = 0;

for(int j=0;j<al.size();j++){

                if(j==0){

                    pre=re[0];

                    re[0]+=al.get(j);

                    min=re[0];

                    continue;

                }

                if(j==al.size()-1){

                    re[j]=pre+al.get(j);

                    if(re[j]<min)

                        min=re[j];

                    continue;

                }

                int temp = re[j];

                re[j]=Math.min(pre, re[j])+al.get(j);

                pre = temp;

                if(re[j]<min)

                    min=re[j];

            }
}

        return min;
}

}

【LeetCode】Triangle