leetcode 120. Triangle
2017-11-03 09:56
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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.
很明显的动态规划,当前总值只和上面的左右有关系,一次遍历就搞定
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.
很明显的动态规划,当前总值只和上面的左右有关系,一次遍历就搞定
class Solution { public: int minimumTotal(vector<vector<int>>& tri) { for(int i=1;i<tri.size();i++) { tri[i][0] += tri[i-1][0]; tri[i][i] += tri[i-1][i-1]; for (int j = 1; j < i; j++) tri[i][j] += min(tri[i-1][j-1], tri[i-1][j]); } return *min_element(tri[tri.size() - 1].begin(), tri[tri.size() - 1].end()); } };
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