From d4431d7c33754d06becf527107c1b15e591c051a Mon Sep 17 00:00:00 2001
From: Yam Borodetsky <yam@yam.codes>
Date: Sun, 15 Feb 2026 20:12:51 +0500
Subject: [PATCH 1/2] Refactor `Solution` class into `SolutionSplitPoint` and
 add corresponding unit tests.

---
 .../Solution.java                             | 36 ++----------------
 .../SolutionSplitPoint.java                   | 37 +++++++++++++++++++
 .../SolutionSplitPointTest.java               | 14 +++++++
 3 files changed, 54 insertions(+), 33 deletions(-)
 create mode 100644 src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPoint.java
 create mode 100644 src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPointTest.java

diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
index ae6622d..ab47649 100644
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
+++ b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
@@ -1,37 +1,7 @@
 package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
 
-/**
- * Solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
- *
- * <p>Uses a split-point counting approach to compute minimum deletions in constant space.
- *
- * <ul>
- *   <li><b>Time Complexity:</b> <code>O(n)</code>
- *   <li><b>Space Complexity:</b> <code>O(1)</code>
- * </ul>
- */
-class Solution {
-  /**
-   * Returns the minimum number of deletions to make {@code s} balanced.
-   *
-   * @param s the string of {@code 'a'} and {@code 'b'} characters
-   * @return the minimum number of deletions needed
-   */
-  int minimumDeletions(String s) {
-    int bCount = 0;
-    int aAfter = 0;
-    int bBefore = 0;
-    for (int i = 0; i < s.length(); i++) {
-      if (s.charAt(i) == 'b') {
-        bCount++;
-      } else {
-        aAfter++;
-      }
-      if (aAfter + bBefore > bCount) {
-        bBefore = bCount;
-        aAfter = 0;
-      }
-    }
-    return Math.min(bCount, aAfter + bBefore);
+public class Solution {
+  public int minimumDeletions(String s) {
+    return 0;
   }
 }
diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPoint.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPoint.java
new file mode 100644
index 0000000..327c31f
--- /dev/null
+++ b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPoint.java
@@ -0,0 +1,37 @@
+package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
+
+/**
+ * Solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
+ *
+ * <p>Uses a split-point counting approach to compute minimum deletions in constant space.
+ *
+ * <ul>
+ *   <li><b>Time Complexity:</b> <code>O(n)</code>
+ *   <li><b>Space Complexity:</b> <code>O(1)</code>
+ * </ul>
+ */
+class SolutionSplitPoint {
+  /**
+   * Returns the minimum number of deletions to make {@code s} balanced.
+   *
+   * @param s the string of {@code 'a'} and {@code 'b'} characters
+   * @return the minimum number of deletions needed
+   */
+  int minimumDeletions(String s) {
+    int bCount = 0;
+    int aAfter = 0;
+    int bBefore = 0;
+    for (int i = 0; i < s.length(); i++) {
+      if (s.charAt(i) == 'b') {
+        bCount++;
+      } else {
+        aAfter++;
+      }
+      if (aAfter + bBefore > bCount) {
+        bBefore = bCount;
+        aAfter = 0;
+      }
+    }
+    return Math.min(bCount, aAfter + bBefore);
+  }
+}
diff --git a/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPointTest.java b/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPointTest.java
new file mode 100644
index 0000000..2e58b54
--- /dev/null
+++ b/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionSplitPointTest.java
@@ -0,0 +1,14 @@
+package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+class SolutionSplitPointTest {
+  @ParameterizedTest
+  @MethodSource("codes.yam.leetcode.minimumdeletionstomakestringbalanced.TestCases#cases")
+  void minimumDeletions(String s, int expected) {
+    assertEquals(expected, new SolutionSplitPoint().minimumDeletions(s));
+  }
+}

From 880243976c343fb87907947e40be8901819c86fc Mon Sep 17 00:00:00 2001
From: Yam Borodetsky <yam@yam.codes>
Date: Sun, 15 Feb 2026 21:09:21 +0500
Subject: [PATCH 2/2] Implement space-optimized DP solution for `Minimum
 Deletions to Make String Balanced` and remove unused recursive and memoized
 solutions.

---
 .../Solution.java                             | 25 ++++++++++++++++---
 .../SolutionDp.java                           | 17 ++++++++++---
 .../SolutionMemoized.java                     | 25 -------------------
 .../SolutionRecursive.java                    | 25 -------------------
 .../package-info.java                         | 15 ++++++-----
 .../SolutionMemoizedTest.java                 | 16 ------------
 .../SolutionRecursiveTest.java                | 16 ------------
 7 files changed, 42 insertions(+), 97 deletions(-)
 delete mode 100644 src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoized.java
 delete mode 100644 src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursive.java
 delete mode 100644 src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoizedTest.java
 delete mode 100644 src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursiveTest.java

diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
index ab47649..ff3d2a0 100644
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
+++ b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/Solution.java
@@ -1,7 +1,26 @@
 package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
 
-public class Solution {
-  public int minimumDeletions(String s) {
-    return 0;
+/**
+ * Solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
+ *
+ * <p>Optimizes {@code SolutionDp} by collapsing the DP table into a single variable.
+ *
+ * <ul>
+ *   <li><b>Time Complexity:</b> <code>O(n)</code>
+ *   <li><b>Space Complexity:</b> <code>O(1)</code>
+ * </ul>
+ */
+class Solution {
+  int minimumDeletions(String s) {
+    int bCount = s.charAt(0) == 'b' ? 1 : 0;
+    int minDel = 0;
+    for (int i = 1; i < s.length(); i++) {
+      if (s.charAt(i) == 'b') {
+        bCount++;
+      } else {
+        minDel = Math.min(minDel + 1, bCount);
+      }
+    }
+    return minDel;
   }
 }
diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionDp.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionDp.java
index 453d052..cf15851 100644
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionDp.java
+++ b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionDp.java
@@ -3,7 +3,7 @@
 /**
  * Bottom-up DP solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
  *
- * <p>Flips the memoized recursion into an iterative DP table.
+ * <p>Iterative DP table tracking minimum deletions at each position.
  *
  * <ul>
  *   <li><b>Time Complexity:</b> <code>O(n)</code>
@@ -17,9 +17,18 @@ class SolutionDp {
    * @param s the string of {@code 'a'} and {@code 'b'} characters
    * @return the minimum number of deletions needed
    */
-  @SuppressWarnings("unused")
   int minimumDeletions(String s) {
-    // TODO: Implement bottom-up DP solution
-    throw new UnsupportedOperationException("Not yet implemented");
+    int n = s.length();
+    int[] dp = new int[n];
+    int bCount = s.charAt(0) == 'b' ? 1 : 0;
+    for (int i = 1; i < n; i++) {
+      if (s.charAt(i) == 'b') {
+        dp[i] = dp[i - 1];
+        bCount++;
+      } else {
+        dp[i] = Math.min(dp[i - 1] + 1, bCount);
+      }
+    }
+    return dp[n - 1];
   }
 }
diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoized.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoized.java
deleted file mode 100644
index 63f3a34..0000000
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoized.java
+++ /dev/null
@@ -1,25 +0,0 @@
-package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
-
-/**
- * Memoized solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
- *
- * <p>Same recursive approach as {@code SolutionRecursive}, but caches overlapping subproblems.
- *
- * <ul>
- *   <li><b>Time Complexity:</b> <code>O(n²)</code>
- *   <li><b>Space Complexity:</b> <code>O(n²)</code>
- * </ul>
- */
-class SolutionMemoized {
-  /**
-   * Returns the minimum number of deletions to make {@code s} balanced.
-   *
-   * @param s the string of {@code 'a'} and {@code 'b'} characters
-   * @return the minimum number of deletions needed
-   */
-  @SuppressWarnings("unused")
-  int minimumDeletions(String s) {
-    // TODO: Implement memoized solution
-    throw new UnsupportedOperationException("Not yet implemented");
-  }
-}
diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursive.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursive.java
deleted file mode 100644
index 02e6330..0000000
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursive.java
+++ /dev/null
@@ -1,25 +0,0 @@
-package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
-
-/**
- * Recursive solution for the <b>Minimum Deletions to Make String Balanced</b> problem.
- *
- * <p>At each character, choose to delete it or keep it, exploring all possibilities.
- *
- * <ul>
- *   <li><b>Time Complexity:</b> <code>O(2^n)</code>
- *   <li><b>Space Complexity:</b> <code>O(n)</code> (call stack)
- * </ul>
- */
-class SolutionRecursive {
-  /**
-   * Returns the minimum number of deletions to make {@code s} balanced.
-   *
-   * @param s the string of {@code 'a'} and {@code 'b'} characters
-   * @return the minimum number of deletions needed
-   */
-  @SuppressWarnings("unused")
-  int minimumDeletions(String s) {
-    // TODO: Implement recursive solution
-    throw new UnsupportedOperationException("Not yet implemented");
-  }
-}
diff --git a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/package-info.java b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/package-info.java
index 6f3c1ae..1f181a8 100644
--- a/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/package-info.java
+++ b/src/main/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/package-info.java
@@ -15,21 +15,20 @@
  *       </code> space
  * </ol>
  *
+ * <p><b>Solution progression (split-point, optimized):</b>
+ *
+ * <ol start="3">
+ *   <li>{@code SolutionSplitPoint} — Split-point counting, <code>O(n)</code> time, <code>O(1)
+ *       </code> space
+ * </ol>
+ *
  * <p><b>Solution progression (DP approach):</b>
  *
  * <ol>
- *   <li>{@code SolutionRecursive} — Brute force recursion, <code>O(2^n)</code> time, <code>O(n)
- *       </code> space
- *   <li>{@code SolutionMemoized} — Memoized recursion, <code>O(n²)</code> time, <code>O(n²)</code>
- *       space
  *   <li>{@code SolutionDp} — Bottom-up DP, <code>O(n)</code> time, <code>O(n)</code> space
  *   <li>{@code Solution} — Space-optimized DP, <code>O(n)</code> time, <code>O(1)</code> space
  * </ol>
  *
- * <p><b>TODO:</b> Current {@code Solution} uses a split-point approach. Once the DP progression is
- * implemented, replace it with the cleaner DP formulation (rename current to {@code
- * SolutionSplitPoint}).
- *
  * @see <a href="https://leetcode.com/problems/minimum-deletions-to-make-string-balanced/">Problem
  *     Link</a>
  */
diff --git a/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoizedTest.java b/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoizedTest.java
deleted file mode 100644
index 9cdff75..0000000
--- a/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionMemoizedTest.java
+++ /dev/null
@@ -1,16 +0,0 @@
-package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import org.junit.jupiter.api.Disabled;
-import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.MethodSource;
-
-@Disabled("Not yet implemented")
-class SolutionMemoizedTest {
-  @ParameterizedTest
-  @MethodSource("codes.yam.leetcode.minimumdeletionstomakestringbalanced.TestCases#cases")
-  void minimumDeletions(String s, int expected) {
-    assertEquals(expected, new SolutionMemoized().minimumDeletions(s));
-  }
-}
diff --git a/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursiveTest.java b/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursiveTest.java
deleted file mode 100644
index 68a662c..0000000
--- a/src/test/java/codes/yam/leetcode/minimumdeletionstomakestringbalanced/SolutionRecursiveTest.java
+++ /dev/null
@@ -1,16 +0,0 @@
-package codes.yam.leetcode.minimumdeletionstomakestringbalanced;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import org.junit.jupiter.api.Disabled;
-import org.junit.jupiter.params.ParameterizedTest;
-import org.junit.jupiter.params.provider.MethodSource;
-
-@Disabled("Not yet implemented")
-class SolutionRecursiveTest {
-  @ParameterizedTest
-  @MethodSource("codes.yam.leetcode.minimumdeletionstomakestringbalanced.TestCases#cases")
-  void minimumDeletions(String s, int expected) {
-    assertEquals(expected, new SolutionRecursive().minimumDeletions(s));
-  }
-}