java: add «1963. Minimum Number of Swaps to Make the String Balanced»

URL:	https://leetcode.com/problems/minimum-number-of-swaps-to-make-the-string-balanced/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/minimum-number-of-swaps-to-make-the-string-balanced.java

@@ -0,0 +1,22 @@
+class Solution {
+  public int minSwaps(String s) {
+    var open = 0;
+    for (var c : s.toCharArray()) {
+      switch (c) {
+        case '[':
+          ++open;
+          break;
+        case ']':
+          if (open > 0) {
+            --open;
+          }
+          break;
+        default:
+          /* no-op */
+          break;
+      }
+    }
+
+    return (1 + open) / 2;
+  }
+}