leetcode-pascal triangle I&&II

对于第2个pascal triangle,通过观察可以发现，其实只需要2个额外的变量来记录，于是就设了个tmp数组。

整体有点DP问题中的滚动数组的感觉。

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

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int>> res;
        if (numRows == 0) return res;
        for (int i = 0; i < numRows; i++)
        {
            vector<int> v; v.clear();
            for (int j = 0; j <= i; j++)
            {
                if (j == 0 || j == i) v.push_back(1);
                if (i>0 && j > 0 && j < i)
                {
                    v.push_back(res[i - 1][j] + res[i - 1][j - 1]);
                }
            }
            res.push_back(v);
        }
        return res;///////////忘了返回了，一直找不出错来。
    }
    vector<int> getRow(int rowIndex) {
        vector<int> res(rowIndex+1,0);
        vector<int> tmp(2,0);
        //if (rowIndex == 0) return vector<int>(1,1);
        for (int i = 0; i <= rowIndex; i++)
        {
            tmp[0] = 1; tmp[1] = 1;//别放错位置。之前放到内层的for里了。
            for (int j = 0; j <= i; j++)
            {
                if (j == 0 || j == i)
                    res[j] = 1;
                if (j>0 && j < i)
                {
                    if (j % 2 == 0)
                        tmp[0] = res[j];
                    else if (j % 2 == 1)
                        tmp[1] = res[j];
                    res[j] += tmp[1-j%2];
                }
            }
        }
        return res;
    }
};

void printVV(vector<vector<int>> vv)
{
    for (int i = 0; i < vv.size(); i++)
    {
        for (int j = 0; j < vv[i].size(); j++)
        {
            cout << vv[i][j] << " ";
        }
        cout << endl;
    }
}
int main()
{
    Solution s;
    //vector<vector<int>> vv = s.generate(3);
    vector<int> v = s.getRow(0);
    for (int i = 0; i < v.size(); i++)
    {
        cout << v[i] << " ";
    }
    //printVV(vv);
    return 0;
}