Java 解法, 执行用时: 1ms, 内存消耗: 251KB, 提交时间: 2016-01-18

import java.util.Stack;

public class ChkExpression {
	public boolean chkLegal(String A) {
		Stack<Character> s1 = new Stack<>();
		Stack<Character> s2 = new Stack<>();
		Stack<Character> s3 = new Stack<>();
		for (int i = 0; i < A.length(); ++i) {
			char c = A.charAt(i);
			switch (c) {
			case '{':
				s1.push(c);
				break;
			case '[':
				s2.push(c);
				break;
			case '(':
				s3.push(c);
				break;
			case '}':
				s1.pop();
				break;
			case ']':
				s2.pop();
				break;
			case ')':
				s3.pop();
				break;
			}
		}
		return s1.isEmpty() && s2.isEmpty() && s3.isEmpty();
	}
}

C++ 解法, 执行用时: 2ms, 内存消耗: 416KB, 提交时间: 2021-09-27

class ChkExpression {
public:
    bool chkLegal(string A) {
        stack<char> ch;
        for (int i = 0; i < A.length(); i++) {
            if (A[i] == '{' || A[i] == '[' || A[i] == '(') {
                ch.push(A[i]);
            }
            
            if (A[i] == '}' || A[i] == ']' || A[i] == ')') {
                if (ch.size() == 0) return false;
                ch.pop();
            }
        }
        return ch.size() == 0;
    }
};

C++ 解法, 执行用时: 3ms, 内存消耗: 376KB, 提交时间: 2020-09-05

class ChkExpression {
public:
    bool chkLegal(string A) {
        // write code here
        int num = A.length();
        int arr[8] = {0};
        int num1=0;
        while(num)
        {
            if(A[num1]=='(')
                arr[0]++;
            else if(A[num1]==')')
                arr[1]++;
            else if(A[num1]=='{')
                arr[2]++;
            else if(A[num1]=='}')
                arr[3]++;
            else if(A[num1]=='[')
                arr[4]++;
            else if(A[num1]==']')
                arr[5]++;
            
            num1++;
            num--;
        }
        if(arr[0]==arr[1]&&arr[2]==arr[3]&&arr[4]==arr[5])
            return true;
        else
            return false;
    }
};

C++ 解法, 执行用时: 3ms, 内存消耗: 376KB, 提交时间: 2020-09-04

class ChkExpression {
public:
    bool chkLegal(string A) {
        int num_left_cb = 0;
        int num_left_sb = 0;
        int num_left_p = 0;
        for (int i = 0; i < A.size(); ++i){
            if (A[i] == '{'){
                //if (num_left_p != 0 || num_left_sb != 0)
                    //return false;
                ++num_left_cb;
            }
            else if (A[i] == '['){
                //if (num_left_p != 0)
                    //return false;
                ++num_left_sb;
            }
            else if (A[i] == '('){
                ++num_left_p;
            }
            else if (A[i] == '}'){
                //if (num_left_p != 0 || num_left_sb != 0)
                    //return false;
                if (num_left_cb == 0)
                    return false;
                --num_left_cb;
            }
            else if (A[i] == ']'){
                //if (num_left_p != 0)
                    //return false;
                if (num_left_sb == 0)
                    return false;
                --num_left_sb;
            }
            else if (A[i] == ')'){
                if (num_left_p == 0)
                    return false;
                --num_left_p;
            }
        }
        if (num_left_p == 0 && num_left_cb == 0 && num_left_sb == 0)
            return true;
        else
            return false;
    }
};

C++ 解法, 执行用时: 3ms, 内存消耗: 408KB, 提交时间: 2021-09-01

class ChkExpression {
public:
    bool chkLegal(string A) {
        // write code here
        stack<char> _stack = stack<char>();
        char topChar;

        for(int i = 0; i < A.size(); i++){
            if(A[i] == '{' || A[i] == '[' || A[i] == '('){
                _stack.push(A[i]);
            }

            // if(A[i] == '}'){
            //     topChar = _stack.top();
            //     if(topChar != '{'){
            //         return false;
            //     }
            //     else{
            //         _stack.pop();
            //     }
            // }
            // else if(A[i] == ']'){
            //     topChar = _stack.top();
            //     if(topChar != '['){
            //         return false;
            //     }
            //     else{
            //         _stack.pop();
            //     }
            // }
            // else if(A[i] == ')'){
            //     topChar = _stack.top();
            //     if(topChar != '('){
            //         return false;
            //     }
            //     else{
            //         _stack.pop();
            //     }
            // }

            if(A[i] == '}' || A[i] == ']' || A[i] == ')'){
                topChar = _stack.top();
                if(topChar == '{' || topChar == '[' || topChar == '('){
                    _stack.pop();
                }
                else{
                    return false;
                }
            }

        }

        if(_stack.size() != 0){
            return false;
        }
        else{
            return true;
        }
    }
};