class Solution {    public int calculateMinimumHP(int[][] dungeon) {        if(dungeon.length==0||dungeon[0].length==0)            return 0;        int M=dungeon.length;        int N=dungeon[0].length;        int[][] dp=new int[M][N];        for(int i=M-1;i>=0;i--)            for(int j=N-1;j>=0;j--)            {                if(i==M-1&&j==N-1)                    dp[i][j]=1-dungeon[i][j];                else if(i==M-1)                    dp[i][j]=dp[i][j+1]-dungeon[i][j];                else if(j==N-1)                    dp[i][j]=dp[i+1][j]-dungeon[i][j];                else                    dp[i][j]=Math.min(dp[i+1][j],dp[i][j+1])-dungeon[i][j];                if(dp[i][j]<=0)                    dp[i][j]=1;            }        return dp[0][0];    }}