[YoungSeok-Choi] week 6 solutions

valid-parentheses/YoungSeok-Choi.java

@@ -0,0 +1,33 @@
+import java.util.Stack;
+
+// TC: O(n)
+class Solution {
+    Stack<Character> st = new Stack<>();
+    public boolean isValid(String s) {
+        for(char c : s.toCharArray()) {
+            if(st.empty() || !isClosing(c)) {
+                st.push(c);
+                continue;
+            }
+
+            char temp = st.peek();
+            if(temp == '(' && c == ')') {
+               st.pop(); 
+            } else if(temp == '[' && c == ']') {
+               st.pop();
+            } else if(temp == '{' && c == '}') {
+                st.pop();
+            } else {
+                st.push(c);
+            }
+        }
+
+        return st.empty();
+    }
+
+    public boolean isClosing(char c) {
+        if(c == ')' || c == ']' || c == '}') return true;
+
+        return false;
+    }
+}