Create SortColors.java

Author: Trmpsanjay

SortColors.java

@@ -0,0 +1,39 @@
+class Solution {
+    /*
+    A rather straight forward solution is a two-pass algorithm using counting sort.
+    First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array
+    with total number of 0's, then 1's and followed by 2's.
+    
+    */
+    public void sortColors(int[] nums) {
+        
+        
+        // pointer soln
+        int i=0,nextZero=0,nextTwo=nums.length-1;
+        while(i<=nextTwo){
+            // if zero tthen swap i with nextzero
+            if(nums[i]==0){
+                int temp=nums[i];
+                nums[i]=nums[nextZero];
+                nums[nextZero]=temp;
+                i++;
+                nextZero++;
+            }
+            // if zero tthen swap i with nextTwo
+            else if(nums[i]==2){
+                int temp=nums[i];
+                nums[i]=nums[nextTwo];
+                nums[nextTwo]=temp;
+                //i++;    // here is the biggest mistake
+                nextTwo--;
+            }
+            //if one then just increase i don't do anything
+           else {
+                i++;
+            }
+            
+            
+        }
+        
+    }
+}