Add C Solution for 20-Valid-Parenthesis

Author: th-blitz

c/20-Valid-Parenthesis.c

@@ -0,0 +1,78 @@
+
+struct Node {
+    char val;
+    struct Node* next;
+};
+
+struct Stack {
+    struct Node* head;
+    size_t len;
+};
+
+struct Node* Node(char val, struct Node* next) {
+    struct Node* root = (struct Node*)malloc(sizeof(struct Node));
+    root -> next = next;
+    root -> val = val; 
+    return root; 
+}
+
+struct Stack* Stack() {
+    struct Stack* stack = (struct Stack*)malloc(sizeof(struct Stack));
+    stack -> len = 0;
+    stack -> head = NULL;
+    return stack;
+}
+
+void append(struct Stack* stack, char val) {
+    struct Node* node = Node(val, stack -> head); 
+    stack -> head = node;
+    stack -> len += 1;
+}
+
+char pop(struct Stack* stack) {
+    if (stack -> head == NULL) {
+        return NULL;
+    }
+    char val = stack -> head -> val;
+    struct Node* deleteNode = stack -> head;
+    stack -> head = stack -> head -> next;
+    stack -> len -= 1;
+    free(deleteNode);
+    return val;
+}
+
+void freeStack(struct Stack* stack) {
+    while (pop(stack) != NULL) {
+        pop(stack);
+    }
+    free(stack);
+}
+
+char opposite_parenthesis(char closing) {
+    char opening = NULL;
+    if (closing == ')') {
+        opening = '(';
+    } else if (closing == '}') {
+        opening = '{';
+    } else if (closing == ']') {
+        opening = '[';
+    }
+    return opening;
+}
+
+bool isValid(char * s){
+    
+    struct Stack* stack = Stack();
+    char* chr;
+    
+    for (chr = s; *chr != '\0'; chr++) {
+        if (opposite_parenthesis(*chr) == NULL) {
+            append(stack, *chr);
+        } else if (stack -> len != 0 && opposite_parenthesis(*chr) == pop(stack)) {
+            continue;
+        } else {
+            return false;
+        }
+    }
+    return stack -> len == 0;
+}