[Leetcode] 020. Valid parentheses (Easy) (C++/java/python)

Index: [Leetcode] leetcode key index (C++/JAVA/PYTHON/SQL)
Github:https://github.com/illuz/leetcode

020.valid_parentheses (Easy) links：

Title: https://oj.leetcode.com/problems/valid-parentheses/
Code (GitHub): Https://github.com/illuz/leetcode

Test Instructions：

Determines whether a parenthesis string is valid.

Analysis：

Directly with the stack simulation, very simple.
The parentheses matching in Java can be written with if, can also be used, and can be used HashMap<Character, Character> "(){}[]".indexOf(s.substring(i, i + 1) . (This discussion can also be used for C + + and Python)

Here C + + is used if match, Java with IndexOf, Python with Dict.

Code：

C++:

Class Solution {Public:bool IsValid (string s) {stack<char> Stk;int len = s.length (); for (int i = 0; i < len; i++)  {if (s[i] = = ' (' | | s[i] = = ' [' | | s[i] = = ' {') {Stk.push (s[i]);} else {if (Stk.empty ()) return false;if (' stk.top () = = ' (' && S[i] = = ') Stk.pop (); else if (stk.top () = = ' [' && s[i] = = '] ') stk.pop (); else if (stk.top () = = ' {' &am p;& S[i] = = '} ') Stk.pop (); Elsereturn false;}} return Stk.empty ();}};

Java:

public class Solution {public    Boolean isValid (String s) {        stack<integer> Stk = new stack<integer> (); for        (int i = 0; i < s.length (); ++i) {            int pos = "() {}[]". IndexOf (S.substring (i, i + 1));            if (pos% 2 = = 1) {                if (stk.isempty () | | Stk.pop ()! = pos-1)                    return false;            } else {                stk.push (POS);            }        }        return Stk.isempty ();}    }

Python:

Class solution:    # @return A Boolean    def isValid (self, s):        MP = {') ': ' (', '] ': ' [', '} ': ' {'}        STK = []
   
    for ch in s:            if ch in ' ([{':                stk.append (CH)            else:                if not STK or mp[ch]! = Stk.pop ():                    return FALSE
    return not STK
   

[Leetcode] 020. Valid parentheses (Easy) (C++/java/python)