leetcode刷题记录

Posted 2022-03-15 zhangjin1120

LeetCode刷题目录

• leetcode刷题7.整数反转求余算法
• leetcode刷题13.罗马数字转整数HashMap+ArrayList

leetcode刷题7.整数反转求余算法

题目描述

示例1：
输入：x = 123
输出：321

示例 2：
输入：x = -123
输出：-321

示例 3：
输入：x = 120
输出：21

示例 4：
输入：x = 0
输出：0

class Solution 
    public int reverse(int x) 
        if (x == 0||x==Integer.MIN_VALUE) 
            return 0;
        
        
        String num = String.valueOf(x);

        boolean isNagi = false;
        if (num.contains("-")) 
            isNagi = true;
            x = -x;
        
        String resultStr = "";

        while (x / 10 != 0 || x % 10 != 0) 
            resultStr = resultStr + x % 10;
            x = x / 10;
        
        if (isNagi) 
            resultStr = "-" + resultStr;
        
        if (resultStr.isEmpty()) 
            return 0;
        
        long result = Long.valueOf(resultStr);
        if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) 
            return 0;
        
        return (int)result;
    

leetcode刷题13.罗马数字转整数HashMap+ArrayList

题目描述

示例 1:
输入: s = “III”
输出: 3

示例 2:
输入: s = “IV”
输出: 4

示例 3:
输入: s = “IX”
输出: 9

示例 4:
输入: s = “LVIII”
输出: 58
解释: L = 50, V= 5, III = 3.

示例 5:
输入: s = “MCMXCIV”
输出: 1994
解释: M = 1000, CM = 900, XC = 90, IV = 4.

class Solution 
       public static int romanToInt(String s) 
            int result = 0;

            HashMap<String, Integer> charIntMap = new HashMap<>();
            charIntMap.put("I", 1);
            charIntMap.put("V", 5);
            charIntMap.put("X", 10);
            charIntMap.put("L", 50);
            charIntMap.put("C", 100);
            charIntMap.put("D", 500);
            charIntMap.put("M", 1000);
            charIntMap.put("IV", 4);
            charIntMap.put("IX", 9);
            charIntMap.put("XL", 40);
            charIntMap.put("XC", 90);
            charIntMap.put("CD", 400);
            charIntMap.put("CM", 900);


            //拆分
 
            char[] charGroup = s.toCharArray();
            for (int i = 0; i < charGroup.length; i++) 
                //1. I IV IX
                //2. V
                //3. X XL XC
                //4. L
                //5. C CD CM
                //6. D
                //7. M
                char current=charGroup[i];
                String key=" ";
                if (i + 1 < charGroup.length) 
                    char next = charGroup[i + 1];

                    if (current == 'I') 
                        if (next == 'V' || next == 'X') 
                            key="" + current + next;
                            i++;
                         else 
                            key=("" + current);
                        
                     else if (current == 'X') 
                        if (next == 'L' || next == 'C') 
                            key=("" + current + next);
                            i++;
                         else 
                            key=("" + current);
                        
                     else if (current == 'C') 
                        if (next == 'D' || next == 'M') 
                            key=("" + current + next);
                            i++;
                         else 
                            key=("" + current);
                        
                     else 
                        key=("" + current);
                    
                 else 
                    key=("" + current);
                
                //累加
                result += charIntMap.get(key);
            


            return result;