hello-algo/codes/java/chapter_dynamic_programming/climbing_stairs_backtrack.java
Yudong Jin fcbaf101a4
Several bug fixes and improvements (#945)
* Update Dockerfile for code debugging.

* Format Python code using Black.

* Improve dark theme by defining html classes for the figures, animations and cover images.

* Fix several glossary translation.

* Update a code comment.

* Fix climbing_stairs_backtrack: the pruning should not require the sorted choices list.

* Update the code of array and list traversal.

* Fix a rendering issue of README.md

* Update code of list traversal.

* Fix array_definition.png

* Update README.md

* Fix max_capacity_moving_short_board.png

* Fix array.dart

* Fix array.dart

* Fix array.dart

* Fix array.dart
2023-11-14 21:27:35 +08:00

44 lines
1.3 KiB
Java

/**
* File: climbing_stairs_backtrack.java
* Created Time: 2023-06-30
* Author: Krahets (krahets@163.com)
*/
package chapter_dynamic_programming;
import java.util.*;
public class climbing_stairs_backtrack {
/* 回溯 */
public static void backtrack(List<Integer> choices, int state, int n, List<Integer> res) {
// 当爬到第 n 阶时,方案数量加 1
if (state == n)
res.set(0, res.get(0) + 1);
// 遍历所有选择
for (Integer choice : 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 */
public static int climbingStairsBacktrack(int n) {
List<Integer> choices = Arrays.asList(1, 2); // 可选择向上爬 1 或 2 阶
int state = 0; // 从第 0 阶开始爬
List<Integer> res = new ArrayList<>();
res.add(0); // 使用 res[0] 记录方案数量
backtrack(choices, state, n, res);
return res.get(0);
}
public static void main(String[] args) {
int n = 9;
int res = climbingStairsBacktrack(n);
System.out.println(String.format("爬 %d 阶楼梯共有 %d 种方案", n, res));
}
}