【LeetCode】118 & 119 - Pascal's Triangle & Pascal's Triangle II

118 - 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]
]

Solution:

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ret;
        if(numRows==)return ret;
        vector<int> vec(,);
        ret.push_back(vec);
        int i=;
        while(i<numRows){
            vec.clear();
            vec.push_back();
            for(int j=;j<ret[i-].size();j++){
                vec.push_back(ret[i-][j-]+ret[i-][j]);
            }
            vec.push_back();
            ret.push_back(vec);
            i++;
        }
        return ret;
    }
};

119 - 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?

Solution：

class Solution {
public:
    vector<int> getRow(int rowIndex) {
        vector<int> vec(,);
        vector<vector<int>> ret;
        ret.push_back(vec);
        int i=;
        while(i<=rowIndex){
            vec.clear();
            vec.push_back();
            for(int j=;j<ret[i-].size();j++){
                vec.push_back(ret[i-][j-]+ret[i-][j]);
            }
            vec.push_back();
            ret.push_back(vec);
            i++;
        }
        return vec;  //or return ret[rowIndex];
    }
};