标签：style blog color io for div 代码 amp
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]
]
思路：对于Pascal三角形的第i行，其两端元素为1，而中间元素Pascal[i][k]=Pascal[i][k-1]+Pascal[i][k]。
1 class Solution { 2 public: 3 vector<vector<int>> generate( int numRows ) { 4 if( numRows <= 0 ) { return vector<vector<int>>(0); } 5 vector<vector<int>> pascals( numRows ); 6 pascals[0].resize( 1, 1 ); 7 for( int i = 1; i < numRows; ++i ) { 8 pascals[i].resize( i+1, 1 ); 9 for( int k = 1; k < i; ++k ) { 10 pascals[i][k] = pascals[i-1][k-1] + pascals[i-1][k]; 11 } 12 } 13 return pascals; 14 } 15 };
另外，Pascal三角形的每一行是对称的，我们可以将上述算法的内层循环进行修改以优化代码。
1 class Solution { 2 public: 3 vector<vector<int>> generate( int numRows ) { 4 if( numRows <= 0 ) { return vector<vector<int>>(0); } 5 vector<vector<int>> pascals( numRows ); 6 pascals[0].resize( 1, 1 ); 7 for( int i = 1; i < numRows; ++i ) { 8 pascals[i].resize( i+1, 1 ); 9 for( int k = 1; k <= i/2; ++k ) { 10 pascals[i][k] = pascals[i][i-k] = pascals[i-1][k-1] + pascals[i-1][k]; 11 } 12 } 13 return pascals; 14 } 15 };
Pascal's Triangle,布布扣,bubuko.com
标签：style blog color io for div 代码 amp
原文地址：http://www.cnblogs.com/moderate-fish/p/3913530.html
