118. Pascal's Triangle

题目描述

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle. In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:
Input: 5
Output: [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]

解题思路

杨辉三角

示例代码

func generate(_ numRows: Int) -> [[Int]] {
    if numRows == 0 {
        return []
    }
    var result: [[Int]] = []
    for i in 1...numRows {
        var temp: [Int] = Array.init(repeating: 0, count: i)
        for j in 0..<i {
            if j == 0 || j == (i-1) {
                temp[j] = 1
            }else {
                let lastLine = result[i-2]
                temp[j] = lastLine[j-1] + lastLine[j]
            }
        }
        result.append(temp)
    }
    return result
}