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Update the code of permutations i and ii

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krahets
2023-04-27 01:18:18 +08:00
parent 918380b56a
commit 3f430fb85e
7 changed files with 91 additions and 60 deletions
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25
codes/java/chapter_backtracking/permutations_i.java
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@ -21,24 +21,29 @@ public class permutations_i {
int choice = choices[i];
// 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
if (!selected[i]) {
// 尝试
selected[i] = true; // 做出选择
state.add(choice); // 更新状态
// 尝试：做出选择，更新状态
selected[i] = true;
state.add(choice);
backtrack(state, choices, selected, res);
// 回退
selected[i] = false; // 撤销选择
state.remove(state.size() - 1); // 恢复到之前的状态
// 回退：撤销选择，恢复到之前的状态
selected[i] = false;
state.remove(state.size() - 1);
}
}
}
/* 全排列 I */
static List<List<Integer>> permutationsI(int[] nums) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
backtrack(new ArrayList<Integer>(), nums, new boolean[nums.length], res);
return res;
}
public static void main(String[] args) {
int[] nums = { 1, 2, 3 };
List<List<Integer>> res = new ArrayList<List<Integer>>();
// 回溯算法
backtrack(new ArrayList<Integer>(), nums, new boolean[nums.length], res);
List<List<Integer>> res = permutationsI(nums);
System.out.println("输入数组 nums = " + Arrays.toString(nums));
System.out.println("所有排列 res = " + res);
}

25
codes/java/chapter_backtracking/permutations_ii.java
View File

@ -10,7 +10,7 @@ import java.util.*;
public class permutations_ii {
/* 回溯算法：全排列 II */
public static void backtrack(List<Integer> state, int[] choices, boolean[] selected, List<List<Integer>> res) {
static void backtrack(List<Integer> state, int[] choices, boolean[] selected, List<List<Integer>> res) {
// 当状态长度等于元素数量时，记录解
if (state.size() == choices.length) {
res.add(new ArrayList<Integer>(state));
@ -22,24 +22,29 @@ public class permutations_ii {
int choice = choices[i];
// 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
if (!selected[i] && !duplicated.contains(choice)) {
// 尝试
// 尝试：做出选择，更新状态
duplicated.add(choice); // 记录选择过的元素值
selected[i] = true; // 做出选择
state.add(choice); // 更新状态
selected[i] = true;
state.add(choice);
backtrack(state, choices, selected, res);
// 回退
selected[i] = false; // 撤销选择
state.remove(state.size() - 1); // 恢复到之前的状态
// 回退：撤销选择，恢复到之前的状态
selected[i] = false;
state.remove(state.size() - 1);
}
}
}
/* 全排列 II */
static List<List<Integer>> permutationsII(int[] nums) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
backtrack(new ArrayList<Integer>(), nums, new boolean[nums.length], res);
return res;
}
public static void main(String[] args) {
int[] nums = { 1, 2, 2 };
List<List<Integer>> res = new ArrayList<List<Integer>>();
// 回溯算法
backtrack(new ArrayList<Integer>(), nums, new boolean[nums.length], res);
List<List<Integer>> res = permutationsII(nums);
System.out.println("输入数组 nums = " + Arrays.toString(nums));
System.out.println("所有排列 res = " + res);