add 0020 solution

Author: luojing

src/com/blankj/easy/_0020/LJSolution.java

@@ -0,0 +1,32 @@
+package com.blankj.easy._020;
+
+/**
+ * @author luojing
+ * @description LJSolution
+ * @date 2022/07/17
+ */
+
+public class LJSolution {
+    public boolean isValid(String s) {
+        char[] stack = new char[s.length() + 1];
+        int top = 1; //top从1开始，避免--top的数组越界Exception的发生
+        for (char c : s.toCharArray()) {
+            if (c == '(' || c == '[' || c == '{') {
+                stack[top++] = c;
+            } else if (c == ')' && stack[--top] != '(') {
+                return false;
+            } else if (c == ']' && stack[--top] != '[') {
+                return false;
+            } else if (c == '}' && stack[--top] != '{') {
+                return false;
+            }
+        }
+        return top == 1;
+    }
+
+    public static void main(String[] args) {
+        LJSolution ljSolution = new LJSolution();
+        System.out.println(ljSolution.isValid("()[]{}({[]})"));
+        System.out.println(ljSolution.isValid("(])]"));
+    }
+}

src/com/blankj/easy/_0020/Solution.java

@@ -23,7 +23,7 @@ public boolean isValid(String s) {
                 return false;
             }
         }
-        return top == 1;
+        return top == 1; //防止奇数个括号返回true的情形出现
     }
 
     public static void main(String[] args) {