Top 150 · 栈（5 题）

class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        int n = s.length();
        stack.push(s.charAt(0));
        for (int i = 1; i < n; i++) {
            char cur = s.charAt(i);
            if(cur == '(' || cur == '{' || cur == '['){
                stack.push(cur);
                continue;
            }
            if(stack.isEmpty())return false;
            char inStack = stack.pop();
            if(cur == ')'){
                if(inStack == '('){
                    continue;
                }else{
                    return false;
                }
            }
            if(cur == '}'){
                if(inStack == '{'){
                    continue;
                }else{
                    return false;
                }
            }
            if(cur == ']'){
                if(inStack == '['){
                    continue;
                }else{
                    return false;
                }
            }
        }
        return stack.isEmpty();
    }
}

class Solution {
    public String simplifyPath(String path) {
        String[] strs = path.split("/");
        Stack<String> stack = new Stack<>();
        for (String s : strs) {
            if(s.isEmpty() || s.equals(".")){
                continue;
            }
            if(!s.equals("..")){
                stack.add(s);
            }else if(!stack.isEmpty()){
                stack.pop();
            }
        }
        StringBuilder sb = new StringBuilder();
        for (String dir : stack) {
            sb.append("/").append(dir);
        }
        return sb.length() == 0 ? "/" : sb.toString();
    }
}

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