Create 60-Permutation-Sequence.java

Author: SharmaTushar1

java/60-Permutation-Sequence.java

@@ -0,0 +1,83 @@
+//Tricky problem but easy
+//this video was helpful https://www.youtube.com/watch?v=wT7gcXLYoao&ab_channel=takeUforward
+
+class Solution {
+    //Time complexity O(N^2) becuase of remove method
+    public String getPermutation(int n, int k) {
+        StringBuilder kthPerm = new StringBuilder();
+        int fact = 1;
+        //this list will contain all the values from 1 to n for reference
+        ArrayList<Integer> list = new ArrayList<>();
+        for (int i = 1; i<n; i++) {
+            fact = fact*i;
+            list.add(i);
+        }
+        list.add(n);
+        k--;
+        while (true) {
+            kthPerm.append(list.get(k/fact)); 
+            list.remove(k/fact);
+            if (list.size()==0)
+                break;
+            k = k%fact;
+            fact = fact/(list.size());
+        }
+        return kthPerm.toString();
+    }
+    
+    {
+        //Bruteforce solution (gives TLE) similar to Next Permutation problem no.31
+      
+//         public String getPermutation(int n, int k) {
+//         int[] num = new int[n];
+//         for (int i = 1; i<=n; i++) {
+//             num[i-1] = i;
+//         }
+//         for (int i = 1; i<k; i++) {
+//             nextPermutation(num);
+//         }
+//         return numToString(num);
+//     }
+    
+//     public void nextPermutation(int[] nums) {
+//         int pivot = nums.length-1;
+//         while (pivot>0 && nums[pivot]<nums[pivot-1]) {
+//             pivot--;
+//         }
+//         pivot--;
+//         int j = nums.length-1;
+//         while (j>0 && nums[j]<nums[pivot]) {
+//             j--;
+//         }
+//         System.out.println(pivot+" "+j);
+//         swap(nums, j, pivot);
+//         reverse(nums, pivot+1);
+//     }
+    
+//     public void reverse(int[] num, int start) {
+//         int end = num.length-1;
+//         while (start<end) {
+//             int temp = num[start];
+//             num[start] = num[end];
+//             num[end] = temp;
+//             start++;
+//             end--;
+//         }
+//     }
+    
+//     public void swap(int[] num, int i, int j) {
+//         int temp = num[i];
+//         num[i] = num[j];
+//         num[j] = temp;
+//     }
+    
+//     public String numToString(int[] arr) {
+//         StringBuilder sb = new StringBuilder();
+//         for (int num: arr) 
+//             sb.append(num);
+//         return sb.toString();
+//     }
+ 
+    }
+    
+}