Pascal & #39; s Triangle I, II, pascaltriangle

Pascal's Triangle I, II, pascaltriangle

The question is from Leetcode.

Https://leetcode.com/problems/pascals-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]]

class Solution {public:    vector<vector<int>> generate(int numRows) {        vector<vector<int> >res;        for(int i=0;i<numRows;i++)        {            vector<int>vec(i+1,1);            if(i>1)                for(int j=1;j<i;j++)                    vec[j]=res[i-1][j-1]+res[i-1][j];            res.push_back(vec);            vector<int>().swap(vec);        }        return res;    }};

Pascal's Triangle II Total Accepted: 42320 Total submission: 143760

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return[1,3,3,1].

Note:
Cocould you optimize your algorithm to use only O (k) extra space?

There are memory requirements here, although the first method can be used for ac, but obviously does not meet the requirements

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<vector<int> >res;        for(int i=0;i<rowIndex+1;i++)        {            vector<int>vec(i+1,1);            if(i>1)                for(int j=1;j<i;j++)                    vec[j]=res[i-1][j-1]+res[i-1][j];            res.push_back(vec);            vector<int>().swap(vec);        }        return res[rowIndex];        }};

We must redesign the algorithm. The first thought is that the coefficient of the pascal triangle is equal to the value of column I in N rows. (R N)
However

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int>res(rowIndex+1,1);        if(rowIndex<2)        return res;       long long nth=1;         for(int i=1;i<rowIndex+1;i++)            nth*=i;         long long rth=1,n_rth=nth;        for(int i=1;i<rowIndex;i++)        {            n_rth/=(rowIndex-i+1);            res[i]=nth/rth/n_rth;                        rth*=(i+1);        }          return res;    }};

When rowIndex = 24, an error is reported. The last correct method is to use the allocated space to calculate the specific description of k = 5.

class Solution {public:    vector<int> getRow(int rowIndex) {        vector<int>res(rowIndex+1,1);        if(rowIndex<2)        return res;        int t1,t2;   for(int i=2;i<=rowIndex;i++)    {        t1=res[0];        t2=res[1];        for(int j=1;j<i+1;j++)        {            res[j]=t1+t2;            t1=t2;            t2=res[j+1];        }        res[i]=1;    }        return res;    }};

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