checking valid string when placeholder can be used.

Author: Arjiit

Strings/checkValidString.java

@@ -0,0 +1,32 @@
+class Solution {
+    public boolean checkValidString(String s) {
+        int leftBracket = 0;
+        for (int i=0;  i<s.length(); i++) {
+            if (s.charAt(i) == '(' || s.charAt(i) == '*') {
+                leftBracket++;
+            } else {
+                leftBracket--;
+            }
+                if (leftBracket < 0) {
+            return false;
+        }
+        }
+        
+        if (leftBracket == 0) {
+            return true;
+        }
+        int rightBracket = 0;
+        for (int i=s.length()-1; i>=0; i--) {
+            if (s.charAt(i) == ')' || s.charAt(i) == '*') {
+                rightBracket++;
+            } else {
+                rightBracket--;
+            }
+            if (rightBracket < 0) {
+            return false;
+        }
+        }
+        
+        return true;
+    }
+}