leetcode solution 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

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2
3
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5
6

[
     [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.

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11

class  {
    public int minimumTotal(List<List<Integer>> trangle) {
        int[] dp = new int[trangle.size()+1];
        for(int i = trangle.size()-1; i>=0; i--){
            for(int j=0; j<=i; j++){
                dp[j] = trangle.get(i).get(j) + Math.min(dp[j], dp[j+1]);
            }
        }
        return dp[0];
    }
}

• dp[i] = min(dp[i+1] , dp[i]) + triangle[j][i]