題目描述(Easy)

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

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

題目連結

Example 1:

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

演算法分析

直上而下生成，細節題。

提交程式碼：

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> result;
        if (numRows < 1) return result;
        if (numRows == 1) return vector<vector<int>>{{1}};
        if (numRows == 2) return vector<vector<int>>{{1}, {1, 1}};
        
        result = vector<vector<int>>{{1}, {1, 1}};
        int i = 3;
        
        for (int i = 3; i <= numRows; ++i) {
            vector<int> temp(i, 1);
            for (int j = 1; j < i - 1; ++j) {
                temp[j] = result[i - 2][j - 1] + result[i - 2][j];
            }
            result.push_back(temp);
        }

        return result;
    }
};