0062.cpp

#include <vector>
using namespace std;

class Solution {
public:
    int uniquePaths(int m, int n) {
        vector<vector<int>> dp(m, vector<int>(n, 0));

        dp[0][0] = 1;
        for (int i = 1; i < m; i++)    dp[i][0] = 1;
        for (int j = 1; j < n; j++)    dp[0][j] = 1;

        for (int i = 1; i < m; i++)
        {
            for (int j = 1; j < n; j++)
                dp[i][j] = dp[i][j-1] + dp[i-1][j];
        }

        return dp[m-1][n-1];
    }
};


class Solution {
public:
    int uniquePaths(int m, int n) {
        std::vector<int> aboveRow(n, 1);

        for (int row = 1; row < m; row++) {
            std::vector<int> currentRow(n, 1);
            for (int col = 1; col < n; col++) {
                currentRow[col] = currentRow[col - 1] + aboveRow[col];
            }
            aboveRow = currentRow;
        }

        return aboveRow[n - 1];        
    }
};