Valid_Parentheses.js

// Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

// An input string is valid if:

//     Open brackets must be closed by the same type of brackets.
//     Open brackets must be closed in the correct order.
//     Every close bracket has a corresponding open bracket of the same type.

// Example 1:

// Input: s = "()"
// Output: true

// Example 2:

// Input: s = "()[]{}"
// Output: true

// Example 3:

// Input: s = "(]"
// Output: false

// Constraints:

//     1 <= s.length <= 104
//     s consists of parentheses only '()[]{}'.

/**
 * @param {string} s
 * @return {boolean}
 */
var isValid = function (s) {
  let st = [],
    p = 0;
  for (let key of s) {
    if (key === "(" || key === "[" || key === "{") {
      st.push(key);
      p++;
    } else if (key === ")") {
      if (st[p - 1] === "(") {
        st.pop();
        p--;
      } else return false;
    } else if (key === "}") {
      if (st[p - 1] === "{") {
        st.pop();
        p--;
      } else return false;
    } else if (key === "]") {
      if (st[p - 1] === "[") {
        st.pop();
        p--;
      } else return false;
    }
  }
  if (st.length !== 0) return false;
  else return true;
};