题目传送： ​​https://leetcode.cn/problems/pascals-triangle/​​

运行效率

Leetcode118. 杨辉三角_c++

代码如下：

class Solution {
   public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> result = new ArrayList<>();
        result.add(Arrays.asList(1));
        //处理边界情况
        if (numRows == 1) {
            return  result;
        }

        while (result.size() < numRows) {
            //取出上一行的结果
            List<Integer> list = result.get(result.size() - 1);
            //用于存储本行的结果
            ArrayList<Integer> curList = new ArrayList<>();
            //每行的第一个元素固定是1
            curList.add(1);

            int left = 0;
            int right = 1;
            while (right < list.size()) {
                Integer num1 = list.get(left);
                Integer num2 = list.get(right);
                curList.add(num1 + num2);
                left++;
                right++;
            }
            //每行的最后一个元素固定是1
            curList.add(1);
            result.add(curList);
        }
        return  result;
    }
}