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Copy pathPermutation.java
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83 lines (73 loc) · 2.03 KB
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/*
Given a collection of distinct integers, return all possible permutations.
Example:
Input: [1,2,3]
Output:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]
*
* */
package recusion;
import java.util.ArrayList;
import java.util.List;
public class Permutation {
public static List<List<Integer>> permutation(int[] nums) {
List<List<Integer>> list = new ArrayList<>();
createItem(list, new ArrayList<Integer>(), nums);
return list;
}
private static void createItem(List<List<Integer>> list, List<Integer> item, int[] nums) {
if (item.size() == nums.length) {
list.add(new ArrayList<Integer>(item));
} else {
for (int i = 0; i < nums.length; i++) {
if (item.contains(nums[i])) {
continue;
}
item.add(nums[i]);
createItem(list, item, nums);
item.remove(item.size() - 1);
}
}
}
/**
* permutation2
* @param nums
* @return
*/
public static List<List<Integer>> permutation2(int[] nums) {
List<List<Integer>> list = new ArrayList<>();
createItem2(list, new ArrayList<Integer>(), nums, new boolean[nums.length]);
return list;
}
/**
* 生成方法
* 用boolean控制数组中每个正在操作的项，防止重复打印
* @param list
* @param item
* @param nums
* @param used
*/
private static void createItem2(List<List<Integer>> list, List<Integer> item, int[] nums, boolean[] used) {
if (item.size() == nums.length) {
list.add(new ArrayList<Integer>(item));
} else {
for (int i = 0; i < nums.length; i++) {
if (used[i]) {
continue;
}
item.add(nums[i]);
used[i] = true;
createItem2(list, item, nums, used);
item.remove(item.size() - 1);
used[i] = false;
}
}
}
}