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40 lines
972 B
40 lines
972 B
/**
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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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/* 回溯 */
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void backtrack(List<int> choices, int state, int n, List<int> res) {
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// 當爬到第 n 階時，方案數量加 1
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if (state == n) {
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res[0]++;
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}
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// 走訪所有選擇
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for (int choice in choices) {
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// 剪枝：不允許越過第 n 階
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if (state + choice > n) continue;
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// 嘗試：做出選擇，更新狀態
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backtrack(choices, state + choice, n, res);
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// 回退
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}
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}
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/* 爬樓梯：回溯 */
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int climbingStairsBacktrack(int n) {
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List<int> choices = [1, 2]; // 可選擇向上爬 1 階或 2 階
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int state = 0; // 從第 0 階開始爬
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List<int> res = [];
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res.add(0); // 使用 res[0] 記錄方案數量
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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("爬 $n 階樓梯共有 $res 種方案");
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}
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