hello-algo/codes/dart/chapter_dynamic_programming/climbing_stairs_backtrack.dart

40 lines
972 B
Dart
Raw Normal View History

/**
* File: climbing_stairs_backtrack.dart
* Created Time: 2023-08-11
* Author: liuyuxin (gvenusleo@gmail.com)
*/
/* 回溯 */
void backtrack(List<int> choices, int state, int n, List<int> res) {
// 当爬到第 n 阶时,方案数量加 1
if (state == n) {
res[0]++;
}
// 遍历所有选择
for (int choice in choices) {
// 剪枝:不允许越过第 n 阶
if (state + choice > n) continue;
// 尝试:做出选择,更新状态
backtrack(choices, state + choice, n, res);
// 回退
}
}
/* 爬楼梯:回溯 */
int climbingStairsBacktrack(int n) {
List<int> choices = [1, 2]; // 可选择向上爬 1 阶或 2 阶
int state = 0; // 从第 0 阶开始爬
List<int> res = [];
res.add(0); // 使用 res[0] 记录方案数量
backtrack(choices, state, n, res);
return res[0];
}
/* Driver Code */
void main() {
int n = 9;
int res = climbingStairsBacktrack(n);
print("$n 阶楼梯共有 $res 种方案");
}