目录

• 前言
• 一、LRU（全A）
• • 代码
• 二、合法括号（全A）
• • 代码

前言

这次的笔试题都是牛客原题哦，祝兄弟们都有心仪的offer

一、LRU（全A）

代码

package youzan;
package youzan;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;


public class First { 
    public static void main(String[] args) { 
        int[][] matrix = new int[][]{ { 1, 1, 1}, { 1, 2, 2}, { 1, 3, 2}, { 2, 1}, { 1, 4, 4}, { 2, 2}};
        System.out.println(Arrays.toString(LRU(matrix, 3)));
    }

    public static int[] LRU(int[][] operators, int k) { 
        // write code here
        LinkedHashMap<Integer, Integer> lruMap = new LinkedHashMap<>();
        ArrayList<Integer> res = new ArrayList<>();

        for (int[] oper : operators) { 
            int key = oper[1];
            switch (oper[0]) { 
                case 1:
                    int value = oper[2];
                    if (lruMap.size() < k) { 
                        lruMap.put(key, value);
                    } else { 
                        Iterator it = lruMap.keySet().iterator();
                        lruMap.remove(it.next());
                        lruMap.put(key, value);
                    }
                    break;
                case 2:
                    if (lruMap.containsKey(key)) { 
                        int val = lruMap.get(key);
                        res.add(val);
                        lruMap.remove(key);

                        lruMap.put(key, val);
                    } else { 
                        res.add(-1);
                    }
                    break;
            }
        }
        int[] resArr = new int[res.size()];
        for (int i = 0; i < res.size(); i++) { 
            resArr[i] = res.get(i);
        }
        return resArr;
    }
}

二、合法括号（全A）

代码

package youzan;

import java.util.Deque;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;


public class Second { 
    public static void main(String[] args) { 
// System.out.println(isVaild("123"));
        System.out.println(isVaild("(123)"));
    }

    public static boolean isVaild(String statement) { 
        int len = statement.length();
        
        Map<Character, Character> pairs = new HashMap<Character, Character>();
        pairs.put(')', '(');
        pairs.put(']', '[');
        pairs.put('}', '{');

        Deque<Character> stack = new LinkedList<>();
        for (int i = 0; i < len; i++) { 
            char ch = statement.charAt(i);
            if (pairs.containsKey(ch)) { 
                if (stack.isEmpty() || stack.peek() != pairs.get(ch)) { 
                    return false;
                }
                stack.pop();
            } else if (ch == '(' || ch == '[' || ch == '{') { 
                stack.push(ch);
            }
        }
        return stack.isEmpty();
    }
}