new tasks

Task/Balanced_brackets/Java/balanced_brackets.java

@@ -0,0 +1,50 @@
+public class Brackets {
+    public static boolean checkBrackets(String str){
+        int mismatchedBrackets = 0;
+        for(char ch:str.toCharArray()){
+            if(ch == '['){
+                mismatchedBrackets++;
+            }else if(ch == ']'){
+                mismatchedBrackets--;
+            }else{
+                return false; //non-bracket chars
+            }
+            if(mismatchedBrackets < 0){ //close bracket before open bracket
+                return false;
+            }
+        }
+        return mismatchedBrackets == 0;
+    }
+
+    public static String generate(int n){
+        if(n % 2 == 1){ //if n is odd we can't match brackets
+            return null;
+        }
+        String ans = "";
+        int openBracketsLeft = n / 2;
+        int unclosed = 0;
+        while(ans.length() < n){
+            if(Math.random() >= .5 && openBracketsLeft > 0 || unclosed == 0){
+                ans += '[';
+                openBracketsLeft--;
+                unclosed++;
+            }else{
+                ans += ']';
+                unclosed--;
+            }
+        }
+        return ans;
+    }
+
+    public static void main(String[] args){
+        String[] tests = {"", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"};
+        for(int i = 0; i <= 16; i+=2){
+            String bracks = generate(i);
+            System.out.println(bracks + ": " + checkBrackets(bracks));
+        }
+
+        for(String test: tests){
+            System.out.println(test + ": " + checkBrackets(test));
+        }
+    }
+}