leetcode new problems

leetcode/lc20/OptimalParantheses.cpp

@@ -0,0 +1,18 @@
+class Solution{
+    public:
+        bool isValid(string s){
+            stack<char> st;
+            for(char c : s){
+                if(c=='(' || c == '{' || c == '[') st.push(c);
+                else{
+                    if(st.empty()) return false;
+
+                    char top = st.top();
+                    st.pop();
+
+                    if((c==')' && top!='(') || (c == '}' && top!= '{') || (c == ']' && top!= '[')) return false;
+                }
+            }
+            return st.empty();
+        }
+};

leetcode/lc20/ValidParantheses1.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+    bool isValid(string s) {
+        stack<char> st;
+        unordered_map<char,char> mapping = {{')','('}, {'}','{'}, {']','['}};
+        for(char c: s){
+                if(mapping.find(c) == mapping.end()) st.push(c);
+                else if(!st.empty() && mapping[c] == st.top()) st.pop();
+                else return false;
+
+        }
+        return st.empty();
+
+
+
+    }
+};