Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return [1,3,3,1].

Note:
Could you optimize your algorithm to use only O(k) extra space?

 

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 Array

 

 

方法一：保存所有二位数组

class Solution {
    public:
        vector<int> getRow(int rowIdx) {
            vector<int> curLine;
            vector<vector<int> >  res;
            curLine.push_back(1);
            res.push_back(curLine);
            if( rowIdx == 0)
                return curLine;

            for(int i = 1; i <= rowIdx; i++)
            {
                curLine.clear();
                for(int j = 0; j < res[i-1].size(); j++)
                {
                    if(j == 0)
                        curLine.push_back(1);
                    else
                        curLine.push_back(res[i-1][j-1] + res[i-1][j]);
                }
                curLine.push_back(1);
                res.push_back(curLine);
            }
            return res[rowIdx];
        }
};

 

方法二：cur只和上一行有关，用滚动数组即可实现空间复杂度O（n）

class Solution {
    public:
        vector<int> getRow(int rowIdx) {
            vector<int> preLine;
            vector<int> curLine;

            curLine.push_back(1);

            if(rowIdx == 0)
                return curLine;

            for(int i = 1; i <= rowIdx; i++)
            {
                preLine = curLine;
                curLine.clear();

                for(int j = 0; j < preLine.size(); j++)
                {
                    if(j == 0)
                        curLine.push_back(1);
                    else
                        curLine.push_back(preLine[j-1] + preLine[j]);

                }
                curLine.push_back(1);
            }
            return curLine;
        }
};