Create 0165-compare-version-numbers.java

Author: sanajitjana

Medium/0165-compare-version-numbers.java

@@ -0,0 +1,102 @@
+/**
+ * Question: Compare Version Numbers
+ * Link: https://leetcode.com/problems/compare-version-numbers/
+ *
+ * Description:
+ * Given two version strings, version1 and version2, compare them.
+ * A version string consists of revisions separated by dots '.'.
+ * Each revision is an integer ignoring leading zeros.
+ *
+ * Return:
+ *   - If version1 < version2, return -1
+ *   - If version1 > version2, return 1
+ *   - Otherwise, return 0
+ *
+ * ------------------------------------------------------------------
+ * Approach:
+ * 1. Split both version strings into integer lists by '.'.
+ * 2. Normalize lengths by padding the shorter list with zeros.
+ * 3. Compare the lists index by index:
+ *      - If any revision differs, return -1 or 1 accordingly.
+ *      - If all are equal, return 0.
+ *
+ * ------------------------------------------------------------------
+ * Dry Run:
+ * version1 = "1.01", version2 = "1.001"
+ * list1 = [1, 1], list2 = [1, 1]
+ * Compare:
+ *   index 0: 1 == 1
+ *   index 1: 1 == 1
+ * Final → return 0
+ *
+ * version1 = "1.0.1", version2 = "1"
+ * list1 = [1, 0, 1], list2 = [1, 0, 0] (after padding)
+ * Compare:
+ *   index 0: 1 == 1
+ *   index 1: 0 == 0
+ *   index 2: 1 > 0 → return 1
+ *
+ * ------------------------------------------------------------------
+ * Time Complexity:
+ * O(n + m) where n = length of version1, m = length of version2
+ * (we parse both strings fully once).
+ *
+ * Space Complexity:
+ * O(n + m) for storing split parts in two lists.
+ */
+
+import java.util.*;
+
+class Solution {
+    public int compareVersion(String version1, String version2) {
+        List<Integer> list1 = new ArrayList<>();
+        StringBuilder st = new StringBuilder();
+        for (int i = 0; i < version1.length(); i++) {
+            char ch = version1.charAt(i);
+            if (ch == '.') {
+                list1.add(Integer.parseInt(st.toString()));
+                st = new StringBuilder();
+            } else {
+                st.append(ch);
+            }
+        }
+        list1.add(Integer.parseInt(st.toString()));
+
+        List<Integer> list2 = new ArrayList<>();
+        StringBuilder st2 = new StringBuilder();
+        for (int i = 0; i < version2.length(); i++) {
+            char ch = version2.charAt(i);
+            if (ch == '.') {
+                list2.add(Integer.parseInt(st2.toString()));
+                st2 = new StringBuilder();
+            } else {
+                st2.append(ch);
+            }
+        }
+        list2.add(Integer.parseInt(st2.toString()));
+
+        if (list1.size() > list2.size()) {
+            for (int i = 0; i < list1.size() - list2.size()+1; i++) {
+                list2.add(0);
+            }
+        } else if (list1.size() < list2.size()) {
+            for (int i = 0; i < list2.size() - list1.size()+1; i++) {
+                list1.add(0);
+            }
+        }
+
+        int i = 0, j = 0;
+        while (i < list1.size() && j < list2.size()) {
+            int num1 = list1.get(i);
+            int num2 = list2.get(j);
+            if (num1 < num2) {
+                return -1;
+            } else if (num1 > num2) {
+                return 1;
+            }
+            i++;
+            j++;
+        }
+        return 0;
+    }
+}