leetcode—pascal triangle

1.题目描述

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]
]

 

2.解法分析

这个题目很简单,所以不需要额外的解说,一遍就AC了

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        //by areslipan@163.com
        vector<vector<int> > pascal;

        if(numRows <= 0)return pascal;
        vector<int> firstRow ;
        firstRow.push_back(1);
        pascal.push_back(firstRow);
        if(numRows == 1)return pascal;
        firstRow.push_back(1);
        pascal.push_back(firstRow);
        if(numRows == 2)return pascal;

        for(int i = 2;i<numRows;++i)
        {
            vector<int> curRow;
            curRow.assign(i+1,0);

            curRow[0]= 1;
            curRow[i] =1;

            for(int j =1;j<i;++j)
            {
                curRow[j]=pascal[i-1][j-1]+pascal[i-1][j];
            }

            pascal.push_back(curRow);
        }

        return pascal;

    }
};