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Permutations.java
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executable file
·43 lines (40 loc) · 1.22 KB
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public class Solution {
public ArrayList<ArrayList<Integer>> permute(int[] num) {
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
Arrays.sort(num);
do {
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i : num)
list.add(i);
result.add(list);
} while (nextPermutation(num));
return result;
}
private boolean nextPermutation(int[] num) {
int n = num.length;
int descStart = 0;
for (int i = n - 1; i > 0; i--)
if (num[i] > num[i - 1]) {
descStart = i;
break;
}
if (descStart == 0) // there is no bigger number
return false;
for (int i = n - 1; i >= descStart; i--)
if (num[i] > num[descStart - 1]){
swap(num, i, descStart - 1);
break;
}
reverse(num, descStart, n - 1);
return true;
}
private void reverse(int[] n, int s, int e) {
for (; s < e; s++, e--)
swap(n, s, e);
}
private void swap(int[] n, int i, int j) {
int tmp = n[i];
n[i] = n[j];
n[j] = tmp;
}
}