/** * File: climbing_stairs_dp.swift * Created Time: 2023-07-15 * Author: nuomi1 (nuomi1@qq.com) */ /* Climbing stairs: Dynamic programming */ func climbingStairsDP(n: Int) -> Int { if n == 1 || n == 2 { return n } // Initialize dp table, used to store subproblem solutions var dp = Array(repeating: 0, count: n + 1) // Initial state: preset the smallest subproblem solution dp[1] = 1 dp[2] = 2 // State transition: gradually solve larger subproblems from smaller ones for i in 3 ... n { dp[i] = dp[i - 1] + dp[i - 2] } return dp[n] } /* Climbing stairs: Space-optimized dynamic programming */ func climbingStairsDPComp(n: Int) -> Int { if n == 1 || n == 2 { return n } var a = 1 var b = 2 for _ in 3 ... n { (a, b) = (b, a + b) } return b } @main enum ClimbingStairsDP { /* Driver Code */ static func main() { let n = 9 var res = climbingStairsDP(n: n) print("Climbing \(n) stairs, there are \(res) different solutions") res = climbingStairsDPComp(n: n) print("Climbing \(n) stairs, there are \(res) different solutions") } }