LeetCode-Algorithm-棧

20. Valid Parentheses (Easy)

• 括號匹配
• 20. Valid Parentheses
• 代碼：

public static boolean isValid(String s) {
        Stack<Byte> stack = new Stack<>();
        byte[] bytes = s.getBytes();
        int length = s.length();
        Byte target;
        for (int i = 0; i < length; i++) {
            if (bytes[i] == '(' || bytes[i] == '[' || bytes[i] == '{') {
                stack.push(bytes[i]);
            } else {
                if (stack.isEmpty()) {
                    return false;
                }
                target = stack.pop();
                if ((bytes[i] == ')' && target != '(') ||
                        (bytes[i] == ']' && target != '[') ||
                        (bytes[i] == '}' && target != '{')) {
                    return false;
                }
            }
        }
        return stack.isEmpty();
    }
複製代碼

71. Simplify Path (Medium)

• 計算unix最簡路徑
• 71. Simplify Path
• 代碼：

public static String simplifyPath(String path) {
        Stack<String> stack = new Stack<>();
        String[] paths = path.split("/");
        for (String s : paths) {
            if (s.length() == 0) {
                continue;
            }
            if (".".equals(s)) {
                continue;
            }
            if ("..".equals(s)) {
                if (!stack.isEmpty()) {
                    stack.pop();
                }
                continue;
            }
            stack.push(s);
        }
        if (stack.isEmpty()) {
            return "/";
        }
        Stack<String> secondStack = new Stack<>();
        while (!stack.isEmpty()) {
            secondStack.push(stack.pop());
        }
        StringBuilder sb = new StringBuilder();
        while (!secondStack.isEmpty()) {
            sb.append("/").append(secondStack.pop());
        }
        return sb.toString();
    }
複製代碼