SmallestNearestElement

Author: hemantautomation

src/main/java/org/Stacks/practice/NearestSmallestElement.java

@@ -0,0 +1,43 @@
+package org.Stacks.practice;
+import java.util.ArrayList;
+import java.util.Stack;
+
+/**
+ * @author hemant
+ *
+ * Given an array A, find the nearest smaller element G[i] for every element A[i] in the array such that the element has an index smaller than i.
+ *
+ * More formally,
+ *
+ * G[i] for an element A[i] = an element A[j] such that
+ *
+ * j is maximum possible AND
+ *
+ * j < i AND
+ *
+ * A[j] < A[i]
+ *
+ * Elements for which no smaller element exist, consider next smaller element as -1.
+ */
+public class NearestSmallestElement {
+    public ArrayList<Integer> prevSmaller(ArrayList<Integer> A){
+        ArrayList<Integer> res=new ArrayList<>();
+        Stack<Integer> stack1=new Stack<>();
+
+        for (Integer integer : A) {
+            while (!stack1.isEmpty() && stack1.peek() >= integer) {
+                stack1.pop();
+            }
+            if (!stack1.isEmpty()) {
+                res.add(stack1.peek());
+            } else {
+                res.add(-1);
+            }
+            stack1.add(integer);
+
+
+        }
+        return res;
+    }
+
+}