#Leetcode# 120. Triangle

https://leetcode.com/problems/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.

代码：

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

　　仿佛开始会做 $dp$ 了