120. Triangle

Difficulty: Medium

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, wheren is the total number of rows in the triangle.

class Solution {public:    int minimumTotal(vector<vector<int>>& triangle) {        int size=triangle.size();        vector<int> dp(size, 0);        for(int i=size-2; i>=0; i--)            for(int j=0; j<triangle[i].size(); j++)                triangle[i][j]+=min(triangle[i+1][j],triangle[i+1][j+1]);        return triangle[0][0];    }};

DP: triangle[i][j]+=min(triangle[i+1][j],triangle[i+1][j+1]); 由下到上计算，最后triangle[0][0]即是结果。