Merge pull request #683 from shankr4444/shankr4444-patch-2

Added Solution for LeetCode Problem No. 31

Author: Sirajmolla

LeetCode/31. Next Permutation/Solution.java

@@ -0,0 +1,60 @@
+// https://leetcode.com/problems/next-permutation/
+
+class Solution {
+    public void nextPermutation(int[] nums) {
+        /*
+        Approach:
+        1. We loop from the end to the point where the value of the element is just smaller than the previous digit.
+        2. Then We loop from the end to that point and find the element which is just greater than the element.
+        3. We swap the two elements.
+        4. Finally we reverse the sequence from end to the index of the point + 1;
+        */
+        
+        int lastIndex = nums.length - 2; // For Comparing The Element With the Next Element
+        int swapIndex = nums.length - 1; // For Swapping Value With The Element Just Greater.
+        
+        // Finding The Index Of The First Smaller Element Than Previous
+        while(lastIndex >= 0 && nums[lastIndex] >= nums[lastIndex + 1]){
+            lastIndex--;
+        }
+        
+        // Swapping The Number With The Previous Just Greater Value
+        if(lastIndex >= 0){
+            
+            while(nums[swapIndex] <= nums[lastIndex]){
+                swapIndex--;
+            }
+            
+            swap(nums, lastIndex, swapIndex);
+            
+        }
+        
+        // Reversing All Elements Behind The Number
+        // In The Edge Case Of The Number Being In Descending Order, The Whole Number Will Be Reversed
+        reverse(nums, lastIndex+1);
+        
+    }
+    
+    //Swap Function
+    public void swap(int[] nums, int i, int j){
+        
+        int temp = nums[i];
+        nums[i] = nums[j];
+        nums[j] = temp;
+        
+    }
+    
+    // Reverse Function
+    public void reverse(int[] nums, int i){
+        
+        int j = nums.length - 1;
+        
+        while(i<j){
+            swap(nums, i, j);
+            i++;
+            j--;
+        }
+        
+    }
+    
+}