45 lines
1.2 KiB
Swift
45 lines
1.2 KiB
Swift
/**
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* File: climbing_stairs_backtrack.swift
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* Created Time: 2023-07-15
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* Backtracking */
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func backtrack(choices: [Int], state: Int, n: Int, res: inout [Int]) {
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// When climbing to the nth step, add 1 to the number of solutions
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if state == n {
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res[0] += 1
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}
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// Traverse all choices
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for choice in choices {
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// Pruning: do not allow climbing beyond the nth step
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if state + choice > n {
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continue
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}
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// Attempt: make a choice, update the state
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backtrack(choices: choices, state: state + choice, n: n, res: &res)
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// Retract
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}
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}
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/* Climbing stairs: Backtracking */
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func climbingStairsBacktrack(n: Int) -> Int {
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let choices = [1, 2] // Can choose to climb up 1 step or 2 steps
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let state = 0 // Start climbing from the 0th step
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var res: [Int] = []
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res.append(0) // Use res[0] to record the number of solutions
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backtrack(choices: choices, state: state, n: n, res: &res)
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return res[0]
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}
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@main
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enum ClimbingStairsBacktrack {
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/* Driver Code */
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static func main() {
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let n = 9
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let res = climbingStairsBacktrack(n: n)
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print("Climbing \(n) stairs, there are \(res) different solutions")
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}
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}
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