feat: add java solution to leetcode problem: No.0020

Author: yanglbme

solution/0000-0099/0020.Valid Parentheses/README.md

@@ -64,7 +64,42 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+
+  public boolean isValid(String s) {
+    if (s == null || s == "") {
+      return true;
+    }
+    char[] chars = s.toCharArray();
+    Stack<Character> helper = new Stack<>();
+    for (char c : chars) {
+      if (isLeft(c)) {
+        helper.push(c);
+      } else {
+        if (helper.isEmpty() || !match(helper.pop(), c)) {
+          return false;
+        }
+      }
+    }
+    return helper.isEmpty();
+  }
+
+  private boolean isLeft(char c) {
+    return c == '(' || c == '[' || c == '{';
+  }
+
+  private boolean isRight(char c) {
+    return c == ')' || c == ']' || c == '}';
+  }
+
+  private boolean match(char left, char right) {
+    return (
+      (left == '(' && right == ')') ||
+      (left == '[' && right == ']') ||
+      (left == '{' && right == '}')
+    );
+  }
+}
 ```
 
 ### **...**

solution/0000-0099/0020.Valid Parentheses/README_EN.md

@@ -81,7 +81,42 @@
 ### **Java**
 
 ```java
-
+class Solution {
+
+  public boolean isValid(String s) {
+    if (s == null || s == "") {
+      return true;
+    }
+    char[] chars = s.toCharArray();
+    Stack<Character> helper = new Stack<>();
+    for (char c : chars) {
+      if (isLeft(c)) {
+        helper.push(c);
+      } else {
+        if (helper.isEmpty() || !match(helper.pop(), c)) {
+          return false;
+        }
+      }
+    }
+    return helper.isEmpty();
+  }
+
+  private boolean isLeft(char c) {
+    return c == '(' || c == '[' || c == '{';
+  }
+
+  private boolean isRight(char c) {
+    return c == ')' || c == ']' || c == '}';
+  }
+
+  private boolean match(char left, char right) {
+    return (
+      (left == '(' && right == ')') ||
+      (left == '[' && right == ']') ||
+      (left == '{' && right == '}')
+    );
+  }
+}
 ```
 
 ### **...**

solution/0000-0099/0020.Valid Parentheses/Solution.java

@@ -1,37 +1,36 @@
 class Solution {
-    public boolean isValid(String s) {
-        if (s == null || s == "") {
-            return true;
-        }
-        char[] chars = s.toCharArray();
-        int n = chars.length;
 
-        Stack<Character> stack = new Stack<>();
-        
-        for (int i = 0; i < n; ++i) {
-            char a = chars[i];
-            if (isLeft(a)) {
-                stack.push(a);
-            } else {
-                if (stack.isEmpty() || !isMatch(stack.pop(), a)) {
-                    return false;
-                }
-            }
-        }
-        
-        return stack.isEmpty();
-                
-    }
-    
-    private boolean isMatch(char a, char b) {
-        return (a == '(' && b == ')') || (a == '[' && b == ']') || (a == '{' && b == '}');
-    }
-    
-    private boolean isLeft(char a) {
-        return a == '(' || a == '[' || a == '{';
+  public boolean isValid(String s) {
+    if (s == null || s == "") {
+      return true;
     }
-    
-    private boolean isRight(char a) {
-        return a == ')' || a == ']' || a == '}';
+    char[] chars = s.toCharArray();
+    Stack<Character> helper = new Stack<>();
+    for (char c : chars) {
+      if (isLeft(c)) {
+        helper.push(c);
+      } else {
+        if (helper.isEmpty() || !match(helper.pop(), c)) {
+          return false;
+        }
+      }
     }
-}
+    return helper.isEmpty();
+  }
+
+  private boolean isLeft(char c) {
+    return c == '(' || c == '[' || c == '{';
+  }
+
+  private boolean isRight(char c) {
+    return c == ')' || c == ']' || c == '}';
+  }
+
+  private boolean match(char left, char right) {
+    return (
+      (left == '(' && right == ')') ||
+      (left == '[' && right == ']') ||
+      (left == '{' && right == '}')
+    );
+  }
+}