permutations leetcode 46

Author: C5141506

src/main/problems/java_problem/backtracking/Permutations.java

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+package java_problem.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Permutations {
+    public static void main(String args[]) {
+        int[] nums = new int[]{1, 2, 3};
+        System.out.println(permute(nums));
+    }
+
+    public static List<List<Integer>> permute(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+        int n = nums.length;
+        if (n == 0) return result;
+        for (int i = 0; i < n; i++)
+            generatePermutation(nums, result, i, new ArrayList<>(), n);
+        return result;
+    }
+
+    public static void generatePermutation(int[] nums, List<List<Integer>> result, int index, List<Integer> ls, int n) {
+        if (index == n && result.contains(ls)) return;
+        if (index == n) {
+
+            if (ls.size() == n) {
+                result.add(new ArrayList<>(ls));
+                ls.remove(ls.size() - 1);
+            }
+            return;
+        }
+        for (int i = 0; i < n; i++) {
+            if (!ls.contains(nums[i])) {
+                ls.add(nums[i]);
+                generatePermutation(nums, result, index + 1, ls, n);
+            }
+        }
+
+        if (ls.size() > 0)
+            ls.remove(ls.size() - 1);
+    }
+
+}

src/main/problems/java_problem/backtracking/PermutationsApporoach2.java

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+package java_problem.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PermutationsApporoach2 {
+    public static void main(String args[]) {
+        int[] nums = new int[]{1, 2, 3};
+        System.out.println(new PermutationsSolution().permute(nums));
+    }
+}
+
+class PermutationsSolution {
+
+    public List<List<Integer>> permute(int[] nums) {
+        int n = nums.length;
+        int totalPermutation = fact(n);
+        List<Integer> ls = new ArrayList<>();
+        for (int val : nums)
+            ls.add(val);
+        return findPermutation(totalPermutation, ls);
+    }
+
+    public List<List<Integer>> findPermutation(int totalPermutation, List<Integer> ls) {
+        List<List<Integer>> permutations = new ArrayList<>();
+        for (int i = 0; i < totalPermutation; i++) {
+            List<Integer> numbers = new ArrayList<Integer>(ls);
+            int dividend = i;
+            List<Integer> permutation = new ArrayList<Integer>();
+            for (int divisor = ls.size(); divisor >= 1; divisor--) {
+                int q = dividend / divisor;
+                int r = dividend % divisor;
+                permutation.add(numbers.get(r));
+                numbers.remove(r);
+                dividend = q;
+            }
+            permutations.add(permutation);
+        }
+        return permutations;
+    }
+
+    public static int fact(int n) {
+        if (n == 1) return n;
+        return n * fact(n - 1);
+    }
+}