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题目链接 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, where n is the total number of rows in the triangle.
类别:动态规划类
❌错误思路:第一次写的时候从上往下走,我觉得只要一直在下层的左右选最小的就好了,然后只有21/43用例通过,举一个例子。 [[-1],[2,3],[1,-1,-3]] 如果从上往下走就是-1 -》 2 -》-1 =0,但是expected是-1,正确答案是-1 -》3-》-3 = 0。因为下一层最小不一定能取到后面的最小。
✅正确思路:从倒数第二层往上遍历,对每一个位都走一遍,直接存往下求和的最小值,直到走到最顶端就是最小路径和。
class Solution {
public:
int minimumTotal(vector<vector<int>>& triangle) {
int len1 = triangle.size();
int len2;
for(int i = len1-2 ;i >= 0 ; i--){
len2 = triangle[i].size();
for(int j = 0 ; j < len2 ;j++){
triangle[i][j] += min(triangle[i+1][j],triangle[i+1][j+1]);
}
}
return triangle[0][0];
}
};