LintCode: Triangle

C++

逆推

class Solution {
public:
    /**
     * @param triangle: a list of lists of integers.
     * @return: An integer, minimum path sum.
     */
    int minimumTotal(vector<vector<int> > &triangle) {
        // write your code here
        if (triangle.size() == 0)
            return 0;
            
        vector<int> dp(triangle.size());
        
        dp[0] = triangle[0][0];
        for(int i = 1; i < triangle.size(); i++)
            for(int j = triangle[i].size() - 1; j >= 0; j--)
                if (j == 0)
                    dp[j] = dp[j] + triangle[i][j];
                else if (j == triangle[i].size() - 1)
                    dp[j] = dp[j-1] + triangle[i][j];
                else
                    dp[j] = min(dp[j-1], dp[j]) + triangle[i][j];
                    
        int ret = INT_MAX;
        for(int i = 0; i < dp.size(); i++)
            ret = min(ret, dp[i]);
            
        return ret;  
    }
};

 C++,修改原数组

class Solution {
public:
    /**
     * @param triangle: a list of lists of integers.
     * @return: An integer, minimum path sum.
     */
    int minimumTotal(vector<vector<int> > &triangle) {
        // write your code here
        for (int i = triangle.size() - 2; i >= 0; --i){
          for (int j = 0; j < i + 1; ++j){
            if(triangle[i+1][j] > triangle[i+1][j+1]){
              triangle[i][j] += triangle[i+1][j+1];
            }else{
              triangle[i][j] += triangle[i+1][j];
            }
          }
        }
        return triangle[0][0];
    }
};