一个二维的dp，很熟练了。这个算法的时间复杂度是O（NM），空间复杂度是O（NM）。
python:
class Solution:
def minPathSum(self, grid: List[List[int]]):
lrow, lcol = len(grid), len(grid[0])
for i in range(1, lrow):
grid[i][0] += grid[i-1][0]
for j in range(1, lcol):
grid[0][j] += grid[0][j-1]
print(grid)
for i in range(1, lrow):
for j in range(1, lcol):
grid[i][j] += min(grid[i][j-1], grid[i-1][j])
return grid[-1][-1]PREVIOUSlc022.括号生成
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