[Leetcode] 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).

 

在输入的数组中直接修改，这样就不需要额外的空间了，不知道这样符合题目的本意不，不过已AC。

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