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).

public int minimumTotal(ArrayList<ArrayList<Integer>> triangle) {
if(triangle.size() == 0 || triangle == null){
return -1;
}
if(triangle.get(0).size() == 0 || triangle.get(0) == null){
return -1;
}
int n = triangle.size();
int[][] dp = new int

;

for(int i = 0; i < n; i++){
dp[n - 1][i] = triangle.get(n-1).get(i);
}

for(int i = n - 2; i > 0 ; i--){
for(int j = 0; j < i; j++){
dp[i][j] = Math.min(dp[i + 1][j], dp[i + 1][j + 1]) + triangle.get(i).get(j);
}
}

return dp[0][0];
}

自底向上，dp[i][j]代表从i,j点到底部最小的和