120 Triangle
Given a 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.
Solution:
class Solution {
public:
int minimumTotal(vector<vector<int>>& triangle) {
int n = triangle.size();
if ( n == 0 ) return 0;
if ( n == 1 ) return triangle[0][0];
vector<int> tmp1 = triangle[n-1];
for ( int i = n-2; i >= 0; i-- ) {
vector<int> tmp2;
for ( int j = 0; j <= i; j++ ) tmp2.push_back(triangle[i][j] + min(tmp1[j], tmp1[j+1]));
tmp1 = tmp2;
}
return tmp1[0];
}
};
[
[2],
[3,4],
[6,5,7],
[4,1,8,3]
]
[4,1,8,3] --> [1+6, 1+5, 7+3] -->[6+3, 6+4] --> [9+2]