Enhance readme with Reverse Integer solution details

Added detailed explanation and implementation for the Reverse Integer problem in Java.

Author: javadev

src/main/java/g0001_0100/s0007_reverse_integer/readme.md

@@ -26,4 +26,65 @@ Given a signed 32-bit integer `x`, return `x` _with its digits reversed_. If rev
 
 **Constraints:**
 
-*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
+*   <code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code>
+
+To solve the Reverse Integer problem in Java using a `Solution` class, we'll follow these steps:
+
+1. Define a `Solution` class with a method named `reverse`.
+2. Initialize variables to keep track of the reversed integer (`rev`), the sign of the input integer (`sign`), and the absolute value of the input integer (`x`).
+3. Iterate through each digit of the input integer `x`:
+   - Extract the least significant digit using the modulo operator.
+   - Update the reversed integer `rev` by multiplying it by 10 and adding the extracted digit.
+   - Update `x` by removing the least significant digit using integer division.
+4. Check if the reversed integer `rev` overflows the signed 32-bit integer range. If so, return 0.
+5. Return the reversed integer `rev` with the appropriate sign.
+
+Here's the implementation:
+
+```java
+public class Solution {
+
+    public int reverse(int x) {
+        int rev = 0;
+        int sign = (x < 0) ? -1 : 1;
+        int limit = Integer.MAX_VALUE / 10;
+        int absX = Math.abs(x);
+
+        while (absX > 0) {
+            int digit = absX % 10;
+            absX /= 10;
+
+            if (rev > limit || (rev == limit && digit > 7)) {
+                return 0;
+            }
+
+            if (rev < -limit || (rev == -limit && digit < -8)) {
+                return 0;
+            }
+
+            rev = rev * 10 + digit;
+        }
+
+        return rev * sign;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+
+        // Test cases
+        int x1 = 123;
+        System.out.println("Example 1 Output: " + solution.reverse(x1));
+
+        int x2 = -123;
+        System.out.println("Example 2 Output: " + solution.reverse(x2));
+
+        int x3 = 120;
+        System.out.println("Example 3 Output: " + solution.reverse(x3));
+
+        int x4 = 0;
+        System.out.println("Example 4 Output: " + solution.reverse(x4));
+    }
+}
+```
+
+This implementation provides a solution to the Reverse Integer problem in Java.