Enhance readme with atoi problem solution

Added a detailed explanation and implementation for the String to Integer (atoi) problem in Java.

Author: javadev

src/main/java/g0001_0100/s0008_string_to_integer_atoi/readme.md

@@ -84,6 +84,77 @@ Return the integer as the final result.
 
 Reading stops at the first non-digit character 'w'.
 
+To solve the String to Integer (atoi) problem in Java using a `Solution` class, we'll follow these steps:
+
+1. Define a `Solution` class with a method named `myAtoi`.
+2. Trim leading whitespace from the input string `s`.
+3. Check if the string is empty after trimming. If so, return 0.
+4. Initialize variables to keep track of the sign of the integer (`sign`), the starting index of the numeric characters (`start`), and the result (`result`).
+5. Check if the first character of the trimmed string is `'-'` or `'+'`. Update `sign` accordingly, and move the starting index accordingly.
+6. Iterate through the characters of the trimmed string starting from the `start` index:
+   - Check if the current character is a digit. If not, break the loop.
+   - Convert the character to its numeric value and update the `result`.
+   - Check if the result exceeds the 32-bit integer range. If so, clamp it to the range and return.
+7. Multiply the `result` by the sign and return the final value.
+8. Handle edge cases where the input string is empty, consists of only whitespace, or contains non-numeric characters at the beginning.
+
+Here's the implementation:
+
+```java
+public class Solution {
+
+    public int myAtoi(String s) {
+        s = s.trim();
+        if (s.isEmpty())
+            return 0;
+
+        int sign = 1;
+        int start = 0;
+        long result = 0;
+
+        if (s.charAt(0) == '-' || s.charAt(0) == '+') {
+            sign = (s.charAt(0) == '-') ? -1 : 1;
+            start++;
+        }
+
+        for (int i = start; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (!Character.isDigit(c))
+                break;
+            result = result * 10 + (c - '0');
+            if (result * sign > Integer.MAX_VALUE)
+                return Integer.MAX_VALUE;
+            if (result * sign < Integer.MIN_VALUE)
+                return Integer.MIN_VALUE;
+        }
+
+        return (int) (result * sign);
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+
+        // Test cases
+        String s1 = "42";
+        System.out.println("Example 1 Output: " + solution.myAtoi(s1));
+
+        String s2 = " -42";
+        System.out.println("Example 2 Output: " + solution.myAtoi(s2));
+
+        String s3 = "4193 with words";
+        System.out.println("Example 3 Output: " + solution.myAtoi(s3));
+
+        String s4 = "words and 987";
+        System.out.println("Example 4 Output: " + solution.myAtoi(s4));
+
+        String s5 = "-91283472332";
+        System.out.println("Example 5 Output: " + solution.myAtoi(s5));
+    }
+}
+```
+
+This implementation provides a solution to the String to Integer (atoi) problem in Java.
+
 **Constraints:**
 
 *   `0 <= s.length <= 200`