20. Valid Parentheses

Author: coderbean

src/leetcode/_0_template/Main.java

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+package leetcode._0_template;
+
+import leetcode._19_.ListNode;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println( solution.isValid(""));
+    }
+}
+

src/leetcode/_0_template/Solution.java

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+package leetcode._0_template;
+
+class Solution {
+    public boolean isValid(String s) {
+        return true;
+    }
+}

src/leetcode/_0_template/solution.md

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+package leetcode._20_;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        System.out.println(solution.isValid("["));
+    }
+}
+

src/leetcode/_20_/Main.java

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+package leetcode._20_;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Stack;
+
+class Solution {
+    public boolean isValid(String s) {
+        List<Character> left = Arrays.asList('(', '{', '[');
+        List<Character> right = Arrays.asList(')', '}', ']');
+        Stack<Integer> stack = new Stack<>();
+        for (char c : s.toCharArray()) {
+            if (left.contains(c)) {
+                stack.push(left.indexOf(c));
+            } else if (right.contains(c)) {
+                if (stack.empty() || !stack.pop().equals(right.indexOf(c))) {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        }
+        return stack.empty();
+    }
+}

src/leetcode/_20_/Solution.java

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+### [20\. Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)
+
+Difficulty: **Easy**
+
+
+Given a string containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.
+
+An input string is valid if:
+
+1.  Open brackets must be closed by the same type of brackets.
+2.  Open brackets must be closed in the correct order.
+
+Note that an empty string is also considered valid.
+
+**Example 1:**
+
+```
+Input: "()"
+Output: true
+```
+
+**Example 2:**
+
+```
+Input: "()[]{}"
+Output: true
+```
+
+**Example 3:**
+
+```
+Input: "(]"
+Output: false
+```
+
+**Example 4:**
+
+```
+Input: "([)]"
+Output: false
+```
+
+**Example 5:**
+
+```
+Input: "{[]}"
+Output: true
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public boolean isValid(String s) {
+        List<Character> left = Arrays.asList('(', '{', '[');
+        List<Character> right = Arrays.asList(')', '}', ']');
+        Stack<Integer> stack = new Stack<>();
+        for (char c : s.toCharArray()) {
+            if (left.contains(c)) {
+                stack.push(left.indexOf(c));
+            } else if (right.contains(c)) {
+                if (stack.empty() || !stack.pop().equals(right.indexOf(c))) {
+                    return false;
+                }
+            } else {
+                return false;
+            }
+        }
+        return stack.empty();
+    }
+}
+```
+![](https://ws3.sinaimg.cn/large/006tKfTcgy1g0uh8bio97j30yo0u0jvz.jpg)