solution.cpp

class Solution 
{
public:
    int calculateMinimumHP(vector<vector<int> > &dungeon) 
    {
        int m = dungeon.size();
        int n = dungeon[0].size();
        dungeon[m-1][n-1] = max(0-dungeon[m-1][n-1], 0);
        for (int i = m - 2; i >= 0; --i) 
        {
            dungeon[i][n-1] = max(dungeon[i+1][n-1]-dungeon[i][n-1], 0);
        }
        for (int j = n - 2; j >= 0; --j) 
        {
            dungeon[m-1][j] = max(dungeon[m-1][j+1]-dungeon[m-1][j], 0);
        }
        for (int i = m - 2; i >= 0; --i) 
        {
            for (int j = n - 2; j >= 0; --j) 
            {
                dungeon[i][j] = max(min(dungeon[i][j+1], dungeon[i+1][j])-dungeon[i][j], 0);
            }
        }
        return dungeon[0][0] + 1;
    }
};