Pascal's Triangle I, II

题目链接

https://leetcode.com/problems/pascals-triangle/

https://leetcode.com/problems/pascals-triangle-ii/

 

这两道题都是数组操作，需要注意的是II在I的基础上使用滚动数组存储过往的中间结果，这个思想可以注意一下，一些DP的题目也会用到

 

I's code

class Solution {

public:

    vector<vector<int> > generate(int numRows) {

        vector<vector<int> > res(numRows, vector<int>(1, 1));

        for(int i = 1; i < numRows; i++) {

            for(int j = 1; j <= i; j++) {

                if(res[i - 1].size() > j)

                    res[i].push_back(res[i - 1][j - 1] + res[i - 1][j]);

                else

                    res[i].push_back(res[i - 1][j - 1]);

            }

        }

        return res;

    }

};

 

II's code

class Solution {

public:

    vector<int> getRow(int rowIndex) {

        vector<int> res(rowIndex + 1, 0);

        res[0] = 1;

        for(int i = 1; i <= rowIndex; i++) {

            for(int j = i; j > 0; j--) {

                res[j] = res[j - 1] + res[j];

            }

        }

        return res;

    }

};