Problem

Given an integer rowIndex, return the rowIndexth row of the Pascal’s triangle.

Notice that the row index starts from 0.

In Pascal’s triangle, each number is the sum of the two numbers directly above it.

Constraints:

• 0 <= rowIndex <= 33

Example1

Input: rowIndex = 3
Output: [1,3,3,1]

Example2

Input: rowIndex = 0
Output: [1]

Example3

Input: rowIndex = 1
Output: [1,1]

Solution

普通DP到滚动数组

class Solution {
public:
    vector<int> getRow(int n) {
        vector<vector<int>> f(n+1, vector<int>(n + 1));
        for (int i = 0; i <= n; i ++ ) {
            f[i][0] = f[i][i] = 1;
            for (int j = 1; j < i; j ++ )
                f[i][j] = f[i - 1 ][j - 1] + f[i - 1][j];
        }
        return f[n];
    }
};

class Solution {
public:
    vector<int> getRow(int n) {
        vector<vector<int>> f(2, vector<int>(n + 1));
        for (int i = 0; i <= n; i ++ ) {
            f[i & 1][0] = f[i & 1][i] = 1;
            for (int j = 1; j < i; j ++ )
                f[i & 1][j] = f[i - 1  & 1][j - 1] + f[i - 1 & 1][j];
        }
        return f[n & 1];
    }
};