add 1653

Author: fishercoder1534

Diff for: paginated_contents/algorithms/2nd_thousand/README.md

@@ -151,6 +151,7 @@
 | 1658 | [Minimum Operations to Reduce X to Zero](https://leetcode.com/problems/minimum-operations-to-reduce-x-to-zero/)                                                                              | [Javascript](./javascript/_1658.js), [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1658.java)                                                      || Medium                                              | Greedy                           |
 | 1657 | [Determine if Two Strings Are Close](https://leetcode.com/problems/determine-if-two-strings-are-close/)                                                                                      | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1657.java)                                                                                       | [:tv:](https://youtu.be/-jXQK-UeChU)                | Medium                           | Greedy                                                               |
 | 1656 | [Design an Ordered Stream](https://leetcode.com/problems/design-an-ordered-stream/)                                                                                                          | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1656.java)                                                                                       || Easy                                                | Array, Design                    |
+| 1653 | [Minimum Deletions to Make String Balanced](https://leetcode.com/problems/minimum-deletions-to-make-string-balanced/)                                                                                                                            | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1653.java)                                                                                       || Medium                                              | Array, DP, Stack                 |
 | 1652 | [Defuse the Bomb](https://leetcode.com/problems/defuse-the-bomb/)                                                                                                                            | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1652.java)                                                                                       || Easy                                                | Array                            |
 | 1650 | [Lowest Common Ancestor of a Binary Tree III](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree-iii/)                                                                    | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1650.java)                                                                                       || Medium                                              | HashTable, Binary Tree, Tree     |
 | 1646 | [Get Maximum in Generated Array](https://leetcode.com/problems/get-maximum-in-generated-array/)                                                                                              | [Solution](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/secondthousand/_1646.java)                                                                                       || Easy                                                | Array                            |

Diff for: src/main/java/com/fishercoder/solutions/secondthousand/_1653.java

@@ -0,0 +1,54 @@
+package com.fishercoder.solutions.secondthousand;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+public class _1653 {
+    public static class Solution1 {
+        public int minimumDeletions(String s) {
+            int[][] dp = new int[s.length()][2];
+            int count = 0;
+            //we count the number of 'b's to the left of each index
+            for (int i = 0; i < s.length(); i++) {
+                dp[i][0] = count;
+                if (s.charAt(i) == 'b') {
+                    count++;
+                }
+            }
+            count = 0;
+            //now we count the number of 'a's to the left of each index
+            for (int i = s.length() - 1; i >= 0; i--) {
+                dp[i][1] = count;
+                if (s.charAt(i) == 'a') {
+                    count++;
+                }
+            }
+            int deletions = s.length();
+            //we can balance the string by deleting all 'b's to the left and all 'a's to the right at each index
+            for (int i = 0; i < s.length(); i++) {
+                deletions = Math.min(deletions, dp[i][0] + dp[i][1]);
+            }
+            return deletions;
+        }
+    }
+
+    public static class Solution2 {
+        /**
+         * use stack
+         * whenever we encounter a "ba" pair, we increase deletions count by one
+         */
+        public int minimumDeletions(String s) {
+            Deque<Character> stack = new LinkedList<>();
+            int deletions = 0;
+            for (char c : s.toCharArray()) {
+                if (!stack.isEmpty() && stack.peekLast() == 'b' && c == 'a') {
+                    stack.pollLast();
+                    deletions++;
+                } else {
+                    stack.addLast(c);
+                }
+            }
+            return deletions;
+        }
+    }
+}

Diff for: src/test/java/com/fishercoder/secondthousand/_1653Test.java

@@ -0,0 +1,31 @@
+package com.fishercoder.secondthousand;
+
+import com.fishercoder.solutions.secondthousand._1653;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class _1653Test {
+    private static _1653.Solution1 solution1;
+    private static _1653.Solution2 solution2;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _1653.Solution1();
+        solution2 = new _1653.Solution2();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(2, solution1.minimumDeletions("aababbab"));
+        assertEquals(2, solution2.minimumDeletions("aababbab"));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(0, solution1.minimumDeletions("aaabbb"));
+        assertEquals(0, solution2.minimumDeletions("aaabbb"));
+    }
+
+}