Solution to Pick from Both Sides

deepcodingios · deepcodingios · commit 4cd42c71ef66 · 2023-03-18T13:31:16.000+05:30
diff --git a/src/Arrays/PrefixSumProblems.java b/src/Arrays/PrefixSumProblems.java
@@ -6,7 +6,13 @@
 public class PrefixSumProblems {
     public static void main(String[] args) {
 
-        int [] array = {1,2,3,4,5};
+        int [] array = {2, 3, -1, 4, 2, 1};
+        int [] array_1 = {-533, -666, -500, 169, 724, 478, 358, -38, -536, 705, -855, 281, -173, 961, -509, -5, 942, -173, 436, -609, -396, 902, -847, -708, -618, 421, -284, 718, 895, 447, 726, -229, 538, 869, 912, 667, -701, 35, 894, -297, 811, 322, -667, 673, -336, 141, 711, -747, -132, 547, 644, -338, -243, -963, -141, -277, 741, 529, -222, -684, 35};
+        System.out.println(pickFromBothSides(array_1,48));
+
+
+        System.out.println(Arrays.toString(suffixArray(array)));
+
         System.out.println(Arrays.toString(prefixSum(array)));
 
         ArrayList<Integer> arrayList = new ArrayList<>(100);
@@ -41,6 +47,83 @@ public static void main(String[] args) {
         return prefixArray;
     }
 
+    static int prefixSumBetweenIndices(int [] A, int start, int end){
+        int [] prefixArray = new int[A.length];
+
+        prefixArray[0] = A[start];
+        int sum = prefixArray[0];
+
+        for (int i = start+1; i < end; i++){
+            sum = sum + A[i];
+            prefixArray[i] = sum;
+        }
+
+        return sum;
+    }
+
+    static int [] suffixArray(int [] array){
+        int [] suffixArray = new int[array.length];
+
+//        suffixArray[array.length-1] = array[array.length-1];
+        int sum = 0;
+
+        for (int i = array.length-1; i >= 0; i--){
+            sum = sum + array[i];
+            suffixArray[i] = sum;
+        }
+
+        System.out.println(Arrays.toString(suffixArray));
+
+        return suffixArray;
+    }
+
+    static int pickFromBothSides(int [] A, int B){
+
+        int N = A.length;
+
+        int [] prefixArray = new int[A.length];
+
+        prefixArray[0] = A[0];
+        int totalSum = prefixArray[0];
+
+        for (int i = 1; i < A.length; i++){
+            totalSum = totalSum + A[i];
+            prefixArray[i] = totalSum;
+        }
+
+        if (N == B){
+            return totalSum;
+        }
+
+        int [] suffixArray = suffixArray(A);
+
+        int start = B-1;
+        int end = N-1;
+
+        int final_answer = Integer.MIN_VALUE;
+
+        while (start >= 0){
+            int answer = 0;
+            if (start == B-1){
+                answer = prefixArray[start];
+                start --;
+            } else {
+                answer = prefixArray[start] + suffixArray[end];
+                System.out.println("Answer is "+ answer);
+                start --;
+                end --;
+            }
+
+            final_answer = Math.max(answer,final_answer);
+        }
+
+        if (end == N-B) {
+            int answer_1 = suffixArray[end];
+            final_answer = Math.max(answer_1,final_answer);
+        }
+        return final_answer;
+    }
+
     static int pickMaxSumFromBothSidesInArray(ArrayList<Integer>list){
 
         int maxSum = list.get(0);
