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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?

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int> ret;          for(int i = 0; i <= rowIndex; i++){              if(i == 0) {                  ret.push_back(1);                  continue;              }                          for(int j = i; j >= 0; j--){    // from end to begin                  if(j == 0) {                      ret[0] = 1;                  } else if(j == i){                      ret.push_back(1);                  }else {                      ret[j] = ret[j-1] + ret[j];                  }              }          }         return ret;    }};

 

Pascal's Triangle II