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🐱(dynamic): 64. 最小路径和

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`@@ -276,6 +276,48 @@ class Solution(object):`
`276`	`276`	- 时间复杂度:`O(m*n)`
`277`	`277`	- 空间复杂度:`O(2n)`
`278`	`278`
	`279`	`+## 64. 最小路径和`
	`280`	`+`
	`281`	`+[原题链接](https://leetcode-cn.com/problems/minimum-path-sum/)`
	`282`	`+`
	`283`	`+### 思路`
	`284`	`+`
	`285`	`+动态规划。`
	`286`	`+`
	`287`	+只能通过该点的左边或是上边到达某个点,因此 `dp[x][y] = min(dp[x - 1][y], dp[x][y - 1]) + grid[x][y]`。
	`288`	`+`
	`289`	`+注意边界处理。`
	`290`	`+`
	`291`	+```python
	`292`	`+class Solution:`
	`293`	`+ def minPathSum(self, grid: List[List[int]]) -> int:`
	`294`	`+ m = len(grid)`
	`295`	`+ if m == 0:`
	`296`	`+ return 0`
	`297`	`+ n = len(grid[0])`
	`298`	`+`
	`299`	`+ dp = [[0 for _ in range(n)] for _ in range(m)]`
	`300`	`+`
	`301`	`+ for i in range(m):`
	`302`	`+ for j in range(n):`
	`303`	`+ if i == 0 and j == 0:`
	`304`	`+ dp[i][j] = grid[i][j]`
	`305`	`+ continue`
	`306`	`+`
	`307`	`+ if i == 0:`
	`308`	`+ dp[i][j] = dp[i][j-1] + grid[i][j]`
	`309`	`+ elif j == 0:`
	`310`	`+ dp[i][j] = dp[i-1][j] + grid[i][j]`
	`311`	`+ else:`
	`312`	`+ dp[i][j] = min(dp[i-1][j], dp[i][j-1]) + grid[i][j]`
	`313`	`+`
	`314`	`+ return dp[m-1][n-1]`
	`315`	+```
	`316`	`+`
	`317`	`+### 复杂度`
	`318`	`+`
	`319`	+- 时间复杂度 `O(m*n)`
	`320`	+- 空间复杂度:`O(m*n)`(如果复用 `grid` 的话也可以达到 `O(1)`)
`279`	`321`
`280`	`322`	`## 70. 爬楼梯`
`281`	`323`

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