Pascal's Triangle

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int>> sols;
        if(numRows==0)return sols;
        vector<int> pre(1,1);
        sols.push_back(pre);
        for(int i=1;i<numRows;i++)
        {
            vector<int> cur;
            cur.push_back(1);
            for(int j=1;j<i;j++)
            {
               cur.push_back(sols[i-1][j-1]+sols[i-1][j]);
            }
            cur.push_back(1);
            sols.push_back(cur);
        }
        return sols;
    }
};

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?

思路：从后往前加就可以利用一个数组。

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> sols(1,1);
        for(int i=1;i<rowIndex+1;i++)
        {
            sols.resize(i+1,0);
            for(int j=sols.size()-1;j>=1;j--)
            {
                sols[j]=sols[j]+sols[j-1];//!!!!
            }
        }
        return sols;
        
    }
};