40 lines
1.0 KiB
Dart
40 lines
1.0 KiB
Dart
/**
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* File: climbing_stairs_backtrack.dart
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* Created Time: 2023-08-11
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* Backtracking */
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void backtrack(List<int> choices, int state, int n, List<int> res) {
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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]++;
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}
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// Traverse all choices
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for (int choice in choices) {
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// Pruning: do not allow climbing beyond the nth step
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if (state + choice > n) continue;
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// Attempt: make a choice, update the state
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backtrack(choices, state + choice, n, 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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int climbingStairsBacktrack(int n) {
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List<int> choices = [1, 2]; // Can choose to climb up 1 step or 2 steps
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int state = 0; // Start climbing from the 0th step
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List<int> res = [];
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res.add(0); // Use res[0] to record the number of solutions
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backtrack(choices, state, n, res);
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return res[0];
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}
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/* Driver Code */
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void main() {
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int n = 9;
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int res = climbingStairsBacktrack(n);
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print("There are $res solutions to climb $n stairs");
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}
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