LeetCode 20. Valid Parentheses 判断()[]{}是否完整

• Total Accepted: 189650
• Total Submissions: 576679
• Difficulty: Easy
• Contributor: LeetCode

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

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

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public boolean isValid(String s) {if(s==null) return false;char[] mid = s.toCharArray();List<Character> store = new ArrayList<Character>();for(char c:mid){if(c=='('||c=='['||c=='{')store.add(c);if(c==')'){if(store.size()>0){if(store.get(store.size()-1)!='(')return false;store.remove(store.size()-1);}else return false;}if(c==']'){if(store.size()>0){if(store.get(store.size()-1)!='[')return false;store.remove(store.size()-1);}elsereturn false;}if(c=='}'){if(store.size()>0){if(store.get(store.size()-1)!='{')return false;store.remove(store.size()-1);}elsereturn false;}}if(store.isEmpty())return true;else return false;}

注意 just the characters，也可以利用栈Stack

public boolean isValid(String s) {Stack<Character> stack = new Stack<Character>();for (char c : s.toCharArray()) {if (c == '(')stack.push(')');else if (c == '{')stack.push('}');else if (c == '[')stack.push(']');else if (stack.isEmpty() || stack.pop() != c)return false;}return stack.isEmpty();}