LeetCode Pascal's Triangle II
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题目
Given an index k, return the kth row of the Pascal's triangle.
For example, given k = 3,
Return [1,3,3,1]
.
Note:
Could you optimize your algorithm to use only O(k) extra space?
与上一题相似,不过只是求特定的某一层,要求只用线性的空间。
第k层的数依次为c(n,0),c(n,1),c(n,2)...c(n,n),
而c(n,i)的递推公式为c(n,i)=c(n,i-1)*(n-i+1)/i,首项c(n,0)为1。
由此递推即可。
代码:
class Solution {public: vector<int> getRow(int rowIndex) { vector<int> ret(1,1);long long temp=1;//每个要压入的数for(int i=1;i<=rowIndex;i++)//递推{temp=temp*(rowIndex-i+1)/i;ret.push_back(temp);}return ret; }};
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