Next Greater using stack

Stack/NextGreater.java

@@ -0,0 +1,48 @@
+package HackerBlocks.Stack;
+
+import java.util.Scanner;
+import java.util.Stack;
+
+public class NextGreater {
+
+	public static void main(String[] args) {
+
+		Scanner scn = new Scanner(System.in);
+		int tc = scn.nextInt();
+		while (tc-- != 0) {
+			int n = scn.nextInt();
+
+			int[] arr = new int[n];
+
+			for(int i=0;i<arr.length;i++) {
+				arr[i]=scn.nextInt();
+			}
+
+			int[] newArr = getNextGreater(arr);
+			for (int i = 0; i < arr.length; i++) {
+				System.out.println(arr[i] + ", " + newArr[i]);
+			}
+		}
+	}
+
+	private static int[] getNextGreater(int[] arr) {
+
+		Stack<Integer> stack = new Stack<Integer>();
+
+		//storing array index in stack
+		stack.push(0);
+		int[] ans = new int[arr.length];
+		for (int i = 1; i < arr.length; i++) {
+
+			while (!stack.isEmpty() && arr[stack.peek()] < arr[i]) {
+				ans[stack.pop()] = arr[i];
+			}
+			stack.push(i);
+		}
+		while (!stack.isEmpty()) {
+			ans[stack.pop()]=-1;
+		}
+		return ans;
+	}
+
+}