118. 杨辉三角

原题

https://leetcode.cn/problems/pascals-triangle/description/

思路

循环

复杂度

时间：O(n²)
空间：O(n²)

Python代码

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        ans = []
        for i in range(1, numRows+1):
            if i == 1:
                ans.append([1])
            else:
                prev = ans[-1]
                curr = []
                for j in range(i):
                    if j == 0 or j == i - 1:
                        curr.append(prev[0])
                    else:
                        curr.append(prev[j-1] + prev[j])
                ans.append(curr)
        return ans 

Go代码

func generate(numRows int) [][]int {
	var ans [][]int
	for i := 1; i <= numRows; i++ {
		if i == 1 {
			ans = append(ans, []int{1})
		} else {
			prev := ans[len(ans)-1]
			curr := []int{}
			for j := 0; j < i; j++ {
				if j == 0 || j == i-1 {
					curr = append(curr, prev[0])
				} else {
					curr = append(curr, prev[j-1]+prev[j])
				}
			}
			ans = append(ans, curr)
		}
	}
	return ans
}