Update Longest Bitonic Sequence.java

Author: py3-coder

DP LIS Pattern/Longest Bitonic Sequence.java

@@ -10,8 +10,9 @@ public static int longestBitonicSequence(int[] arr, int n) {
         //return solveRec(arr, 0, -1,false);
 
         //
-        map =new HashMap<>();
-        return solveMemo(arr,0,-1,false);
+        // map =new HashMap<>();
+        // return solveMemo(arr,0,-1,false);
+        return solveLIS(arr);
     }
     public static int solveRec(int[] arr,int indx ,int prev,boolean flag){
         //Base :::
@@ -36,7 +37,6 @@ public static int solveRec(int[] arr,int indx ,int prev,boolean flag){
             int notpick= solveRec(arr, indx+1, prev, flag);
 
             return Math.max(pick,notpick);
-
         }
     }
     public static int solveMemo(int[] arr,int indx ,int prev,boolean flag){
@@ -68,4 +68,33 @@ public static int solveMemo(int[] arr,int indx ,int prev,boolean flag){
             return Math.max(pick,notpick);
         }
     }
+
+    // Best Soln :: Apprcoch : Could be LIS (arr)  LIS (rev(arr)) ::
+    //Lets SEE ::
+    public static int solveLIS(int arr[]){
+        int n=arr.length;
+        int frontLIS[] =new int[n];
+        int revLIS[] =new int[n];
+        Arrays.fill(frontLIS,1);
+        Arrays.fill(revLIS,1);
+        int maxi=0;
+        for(int i=1;i<n;i++){
+            for(int j=0;j<i;j++){
+                if(arr[i]>arr[j] && 1+frontLIS[j]>frontLIS[i]){
+                    frontLIS[i] =1+frontLIS[j];
+                }
+            }
+        }
+
+       for(int i=n-1;i>=0;i--){
+           for(int j=n-1;j>i;j--){
+               if(arr[i]>arr[j] && 1+revLIS[j]>revLIS[i]){
+                   revLIS[i] =1+revLIS[j];
+               }
+           }
+           maxi =Math.max(maxi,frontLIS[i]+revLIS[i]-1);
+       }
+       return maxi;
+    }
+
 }