118. Pascal's Triangle
2018-03-20 19:14
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Description
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]
]
Solution
class Solution { public: vector<vector<int>> generate(int numRows) { vector<vector<int>> vals; vals.resize(numRows); for(int i = 0; i < numRows; i++) { vals[i].resize(i + 1); vals[i][0] = 1; //首元素及尾元素为1 vals[i][vals[i].size() - 1] = 1; for(int j = 1; j < vals[i].size() - 1; j++) { vals[i][j] = vals[i - 1][j - 1] + vals[i - 1][j]; } } return vals; } };
Analysis
要得到一个帕斯卡三角,我们只需要找到规律即可。1. 第k层有k个元素
2. 每层第一个以及最后一个元素值为1
3. 对于第k(k > 2)层第n(n > 1 && n < k)个元素A[k]
,A[k]
= A[k-1][n-1] + A[k-1]
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