[Leetcode]Triangle

空間O(N^2)

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        for(int i = triangle.size()-2; i >= 0; --i)
            for(int j = 0; j <= i; j++)
                triangle[i][j] += min(triangle[i+1][j], triangle[i+1][j+1]);
        return triangle[0][0];
    }
};

空間優化爲O(N)

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(triangle.empty()) return 0;
        vector<int> f(triangle.back());
        for(int i = triangle.size() - 2; i >= 0; i--)
            for(int j = 0; j <= i; j++)
                f[j] = min(f[j], f[j+1]) + triangle[i][j];
        return f[0];
    }
};