Triangle

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triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

Note:
Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

Solve the Problem on Leetcode

class Solution {
public:
int minimumTotal(vector<vector<int>>& triangle) {
//从下向上
int n=triangle.size();
if(n==0) return 0;
vector<int> res(n,0);
for(int i=0;i<n;i++)
res[i]=triangle[n-1][i];
// if(n==1) return res[0];
for(int i=n-2;i>=0;i--)
{
for(int j=0;j<=i;j++)
{
// res[j]=(res[j]<res[j+1])?res[j]:res[j+1]+triangle[i][j];
if(res[j]<res[j+1])
res[j]=res[j]+triangle[i][j];
else
res[j]=res[j+1]+triangle[i][j];
}
}
return res[0];

}

};