LeetCode OJ——Pascal's Triangle

http://oj.leetcode.com/problems/pascals-triangle/ 杨辉三角

先分析数据，找出规律

ans[row][col] = ans[row-1][col-1]+ans[row-1][col]

#include <iostream>
#include <vector>
#include <string>
using namespace std;

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        vector<vector<int> > ans;
        ans.clear();
        if(numRows<=0)
            return ans;
        //1
        vector<int> onepiece;
        onepiece.push_back(1);
        ans.push_back(onepiece);
        if(numRows == 1)
            return ans;
        //2
        onepiece.clear();
        onepiece.push_back(1);
        onepiece.push_back(1);
        ans.push_back(onepiece);
        if(numRows == 2)
            return ans;

        //3...
        for(int row = 2;row < numRows;row++)
        {
            onepiece.clear();
            for(int col = 0;col <= row;col++)
            {
                if(col ==0 || row == col)
                    onepiece.push_back(1);
                else
                onepiece.push_back(ans[row-1][col-1]+ans[row-1][col]);
            }
            ans.push_back(onepiece);
        }
        return ans;
    }
};

int main()
{
    Solution mysolution;
    mysolution.generate(1);

    return 0;
}