LeetCode开心刷题三十天——64. Minimum Path Sum*70. Climbing Stairs大水题不用看了

64. Minimum Path Sum

Medium

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Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

Example:

Input:
[
  [1,3,1],
  [1,5,1],
  [4,2,1]
]
Output: 7
Explanation: Because the path 1→3→1→1→1 minimizes the sum.
Python version：

class Solution(object):
    def minPathSum(self, grid):
        """
        :type grid: List[List[int]]
        :rtype: int
        """
        m,n=len(grid),len(grid[0])
        dp = [[2147483647] * (n+1) for _ in range(m+1)]
        dp[1][1]=grid[0][0]
        for i in range(1,m+1):
            for j in range(1,n+1):
                if i==j==1:
                    continue
                dp[i][j]=min(dp[i-1][j],dp[i][j-1])+grid[i-1][j-1]
                #print(dp[-1][1])
        return dp[m][n]


solu=Solution()
myList2=[
    [1, 3, 1],
    [1, 5, 1],
    [4, 2, 1]
]
print(solu.minPathSum(myList2))

C++ version:

#include
#include
#include<string>
#include
#include<set>
#include

The difference is it want the min,so we initialize the array should use MAX_INT value 2147483647

We have to make dp larger than vector by +1,only in this way we can better solve the problem i-1 has minus one,if we want to initialize it to 0,it doesn't have matter for reason that it will be auto in 0,but we need it to be the MAX_INT we need the minimum value.So we have to use larger matrix but 63 needn't

70BONUS：

n is the input parameter

Two Attention Point:

1.because we initialize the 0-2 value so must let n+2 or the index may out of range.

2.dp[0] dp[1] this kinds of value need to initial by this way dp=[[0] for _ in range(N+2)]

3.first I let this position is 1000,but when I change into n+2 whole program quick a lot

4.range function can have two parameter (start,end) for i in range(3)---->0,1,2  for i in range(1,3)----->1,2

 

dp=[[0]  for _ in range(n+2)]
        dp[0] = 0
        dp[1] = 1
        dp[2] = 2

 

 

 

转载于:https://www.cnblogs.com/Marigolci/p/11312718.html