杨辉三角

Given a non-negative integer numRows, generate the first numRows of Pascal’s triangle.

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