[leetcode]Dungeon Game

dp，精华是从右下角开始。

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