Pascal's Triangle Pascal's Triangle||

Pascal‘s Triangle:

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]
]

Pascal‘s Triangle||:

Given an index k, return the k^th 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?

Pascal‘s triangle.

public class Solution {
	public List<List<Integer>> generate(int numRows) {
	    if(numRows == 0){
			return new ArrayList<List<Integer>>();
		}
		List<List<Integer>> ans = new ArrayList<List<Integer>>();
		ans.add(new ArrayList<Integer>(Arrays.asList(1)));
		for(int i=1;i<numRows;i++){
			List<Integer> list = new ArrayList<Integer>();
			for(int j=0;j<=i;j++){
				if(j==0||j==i){
					list.add(1);
					continue;
				}
				list.add(ans.get(i-1).get(j-1)+ans.get(i-1).get(j));
			}
			ans.add(list);
		}
		return ans;
	}
}

Pascal‘s Triangle||:

public class Solution {
    	public List<Integer> getRow(int rowIndex) {
		List<Integer> ans = new ArrayList<Integer>();
		for(int i=0;i<=rowIndex;i++){
			List<Integer> temp = new ArrayList<Integer>();
			for(int j=0;j<=i;j++){
				if(j==0||j==i){
					temp.add(1);
					continue;
				}
				temp.add(ans.get(j)+ans.get(j-1));
			}
			ans = new ArrayList<Integer>(temp);
		}
		return ans;
	}
}

其实这些基本处理就是学习C语言时的杨辉三角。

Pascal's Triangle Pascal's Triangle||