Pascal's Triangle

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118.Pascal’s Triangle

Given an integer numRows, return the first numRows of Pascal’s triangle.

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

Example 1:

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Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Example 2:

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Input: numRows = 1
Output: [[1]]

时间复杂度：O(numRows^2^)

空间复杂度：O(1)

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class Solution {
    public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ans_v(numRows);
        for (int i = 0; i < numRows; ++i) {
            ans_v[i].resize(i + 1);
            ans_v[i][0] = 1;
            ans_v[i][i] = 1;
            for (int j = 1; j < i; ++j) {
                ans_v[i][j] = ans_v[i - 1][j] + ans_v[i - 1][j - 1];
            }
        }
        return ans_v;
    }
};