118. Pascal's Triangle java solutions

For example, given numRows = 5,
Return

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

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public class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> ans = new ArrayList<List<Integer>>();
        if(numRows < 1) return ans;
        int r = 0;
        while(r < numRows){
            List<Integer> tmp = new ArrayList<Integer>(r+1);
            if(r == 0){
                tmp.add(1);
            }else{
                int c = 0;
                while(c < r+1){
                    if(c == 0 || c == r) tmp.add(1);
                    else{
                        tmp.add(ans.get(r-1).get(c)+ans.get(r-1).get(c-1));
                    }
                    c++;
                }
            }
            ans.add(tmp);
            r++;
        }
        return ans;
    }
}

根据杨辉三角的数学定义来做。

解法2：

参照Pascal's Triangle 2 的解法。

119. Pascal's Triangle II java solutions