[Swift]LeetCode118. 杨辉三角 | Pascal's Triangle

weixin_30906671

130人浏览 · 2018-09-26 20:03:00

weixin_30906671 · 2018-09-26 20:03:00 发布

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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]
]

给定一个非负整数 numRows，生成杨辉三角的前 numRows 行。

在杨辉三角中，每个数是它左上方和右上方的数的和。

示例:

输入: 5
输出:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

 1 class Solution {
 2     func generate(_ numRows: Int) -> [[Int]] {
 3         var res:[[Int]] =  [[Int]]()
 4         if numRows <= 0 {return res}
 5         var arr:[Int] = [Int]()
 6         arr.append(1)
 7         res.append(arr)
 8         
 9         for i in 1..<numRows
10         {
11             var temp:[Int] = [Int]() 
12             temp.append(1)
13             
14             var count:Int = res[i - 1].count
15             for j in 1..<count
16             {
17                 temp.append(res[i-1][j]+res[i-1][j-1])
18             }
19             temp.append(1)
20             res.append(temp)
21         }
22         return res
23     }
24 }

8ms

 1 class Solution {
 2     func generate(_ numRows: Int) -> [[Int]] {
 3     guard numRows > 0 else {
 4         return []
 5     }
 6     
 7     var temp = [[1]]
 8     for i in 1..<numRows {
 9         let last = temp[i - 1]
10         var arr = [Int]()
11         for j in 0...i {
12             var n : Int
13             if j == 0 {
14                 n = 1
15             }else if j == i {
16                 n = last[j - 1]
17             }else {
18                 n = last[j] + last[j - 1]
19             }
20             arr.append(n)
21         }
22         temp.append(arr)
23     }
24     
25     return temp
26     }
27 }

8ms

 1 class Solution {
 2     func generate(_ numRows: Int) -> [[Int]] {
 3         if numRows == 0 { return [] }
 4         else if numRows == 1 { return [[1]] }
 5         else if numRows == 2 { return [[1], [1,1]] }
 6         
 7         var memo = [[1], [1,1]]
 8         
 9         for i in 1..<numRows-1 {
10             let prevArr = memo[i]
11             var arr = Array(repeating: 0, count: prevArr.count+1)
12             arr[0] = 1
13             arr[arr.count-1] = 1
14 
15             for j in 1..<arr.count-1 {
16                 arr[j] = prevArr[j-1]+prevArr[j]
17             }
18             
19             memo.append(arr)
20         }
21         
22         return memo
23     }
24 }

12ms

 1 class Solution {
 2     func generate(_ numRows: Int) -> [[Int]] {
 3         if numRows == 0 {
 4             return []
 5         }
 6         var result = [[1]]
 7         for i in 1...numRows {
 8             var numRow = [Int]()
 9             var lastNumRow = result[i - 1]
10             for j in 0..<i {
11                 if j == 0 || j == i - 1 {
12                     numRow.append(1)
13                 } else {
14                     numRow.append(lastNumRow[j - 1] + lastNumRow[j])
15                 }
16             }
17             result.append(numRow)
18         }
19         result.remove(at: 0)
20         return result
21     }
22 }