leetcode解题: Pascal's Triangle (118)

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Given numRows, generate the first numRows of Pascal’s triangle.

For example, given numRows = 5,
Return

[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]

解法1： O（N^2) N 是numRows

很基础的题，注意第i层的第j个字符是第i-1层的第j个数和第j-1个数之和就可以了。
C++

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

Java

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