# Dungeon Game

The demons had captured the princess (**P**) and imprisoned her in the bottom-right corner of a dungeon. The dungeon consists of M x N rooms laid out in a 2D grid. Our valiant knight (**K**) was initially positioned in the top-left room and must fight his way through the dungeon to rescue the princess.

The knight has an initial health point represented by a positive integer. If at any point his health point drops to 0 or below, he dies immediately.

Some of the rooms are guarded by demons, so the knight loses health (_negative\_integers) upon entering these rooms; other rooms are either empty (\_0's_) or contain magic orbs that increase the knight's health (\_positive\_integers).

In order to reach the princess as quickly as possible, the knight decides to move only rightward or downward in each step.

**Write a function to determine the knight's minimum initial health so that he is able to rescue the princess.**

For example, given the dungeon below, the initial health of the knight must be at least**7**if he follows the optimal path`RIGHT-> RIGHT -> DOWN -> DOWN`.

| -2 (K) | -3  | 3      |
| ------ | --- | ------ |
| -5     | -10 | 1      |
| 10     | 30  | -5 (P) |

**Note:**

* The knight's health has no upper bound.
* Any room can contain threats or power-ups, even the first room the knight enters and the bottom-right room where the princess is imprisoned.

分析

从右下开始减当前格子，负数设为1，正数继续。 这样的话负格子才会累加，正格子设为1，不做考虑。

```
class Solution:
    def calculateMinimumHP(self, dungeon: List[List[int]]) -> int:
        if not dungeon or not dungeon[0]:
            return 0
        n, m = len(dungeon), len(dungeon[0])

        dp = [[float('inf')] * (m + 1) for i in range(n + 1)]
        dp[n][m-1]=dp[n-1][m]=1
        for i in range(n-1,-1,-1):
            for j in range(m-1,-1,-1):
                temp = min(dp[i + 1][j], dp[i][j + 1])-dungeon[i][j]                
                dp[i][j] = 1 if temp <= 0 else temp                

        return dp[0][0]
```
