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leetcode Pascal's Triangle
给定行号,输出如下所示Pascal Triangle(杨辉三角)
For example, given numRows = 5,
Return
[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]
思路,想到右上一个构建下一个,构成过程就是上一个的相邻元素相加,并且头尾为1.
class Solution {public:vector<int> fun116(vector<int> perm){ vector<int> tmp; tmp.push_back(1); for (int i = 0; i < perm.size() - 1; i++) { tmp.push_back(perm[i] + perm[i + 1]); } tmp.push_back(1); return tmp;}vector<vector<int> > generate(int numRows){ vector<vector<int> > ans; if (numRows == 0) return ans; vector<int> perm(1,1); while(numRows-- > 0) { ans.push_back(perm); perm = fun116(perm); } return ans;}};
也可以这样:
class Solution {public: vector<vector<int> > generate(int numRows) { // Note: The Solution object is instantiated only once and is reused by each test case. vector<vector<int> > res; if(numRows == 0) return res; for(int i = 1; i <= numRows; i++) { vector<int> onelevel; onelevel.clear(); onelevel.push_back(1); for(int j = 1; j < i; j++) { onelevel.push_back(res[i-2][j-1] + (j < i-1 ? res[i-2][j] : 0)); } res.push_back(onelevel); } return res; }};
leetcode Pascal's Triangle
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