[leetcode.com]算法题目

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]
]

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(0 == numRows){
            vector<vector<int> > result;
            return result;
        } 
             
        vector<vector<int> > result(numRows);
        
        vector<int> first(1,1);
        result[0] = first;
        for(int i=1;i<numRows;i++){
            result[i] = nextTriangle(result[i-1]);
        }
        
        return result;    
    }
    
    vector<int> nextTriangle(vector<int> a){
        int k = a.size();
        vector<int> next(k+1);
        for(int i=0;i<k+1;i++){
            if(0==i){
                next[i] = a[i];
                continue;
            }
            if(k==i){
                next[i] = a[k-1];
                continue;
            }
            next[i] = a[i-1]+a[i];
        }
        return next;
    }
};

思路：创建一个函数，使用上一行的vector去计算下一行的vector，然后反复调用即可。需要尤其注意输入的值为0时候的情况。