LeetCode 118 杨辉三角

基本思路  a[i+1][j]=a[i][j-1]+a[i][j]

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<int>a;
        a.push_back(1);
        vector<int>b;
        b.push_back(1);
        b.push_back(1);
        vector<vector<int>>res;
      //  printf("%d",res.size());
        if(numRows==0){
            return res;
        }
        if(numRows==1){
            res.push_back(a);
            return res;
        }
        if(numRows==2){
            res.push_back(a);
            res.push_back(b);
            return res;
        }
        res.push_back(a);
        res.push_back(b);
        for(int i=2;i<numRows;++i){
            vector<int>temp;
            int len=b.size();
            temp.push_back(1);
            for(int j=0;j<len-1;++j){
                int val=b[j]+b[j+1];
                temp.push_back(val);
            }
            temp.push_back(1);
            res.push_back(temp);
            b=temp;
        }
        return res;
    }
};