zoukankan      html  css  js  c++  java
  • 13. Roman to Integer

    Roman numerals are represented by seven different symbols: IVXLCD and M.

    Symbol       Value
    I             1
    V             5
    X             10
    L             50
    C             100
    D             500
    M             1000

    For example, two is written as II in Roman numeral, just two one's added together. Twelve is written as, XII, which is simply X + II. The number twenty seven is written as XXVII, which is XX + V + II.

    Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII. Instead, the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX. There are six instances where subtraction is used:

    • I can be placed before V (5) and X (10) to make 4 and 9. 
    • X can be placed before L (50) and C (100) to make 40 and 90. 
    • C can be placed before D (500) and M (1000) to make 400 and 900.

    Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.

    Example 1:

    Input: "III"
    Output: 3

    Example 2:

    Input: "IV"
    Output: 4

    Example 3:

    Input: "IX"
    Output: 9

    Example 4:

    Input: "LVIII"
    Output: 58
    Explanation: L = 50, V= 5, III = 3.
    

    Example 5:

    Input: "MCMXCIV"
    Output: 1994
    Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

    用hashmap存字符到数字的映射,再遍历string:如果当前字符是最后一个字符,加上当前字符;如果下一个字符<=当前字符,加上当前字符;否则,减去当前字符

    time: O(n), space: O(n)

    class Solution {
        public int romanToInt(String s) {
            HashMap<Character, Integer> map = new HashMap<>();
            map.put('I', 1);
            map.put('V', 5);
            map.put('X', 10);
            map.put('L', 50);
            map.put('C', 100);
            map.put('D', 500);
            map.put('M', 1000);
            
            int res = 0;
            for(int i = 0; i < s.length(); i++) {
                if(i == s.length() - 1) {
                    res += map.get(s.charAt(i));
                } else if(map.get(s.charAt(i+1)) <= map.get(s.charAt(i))){
                    res += map.get(s.charAt(i));
                } else {
                    res -= map.get(s.charAt(i));
                }
            }
            return res;
        }
    }
  • 相关阅读:
    DOS 批处理命令For循环命令详解
    怎样在电脑上下载哔哩哔哩的视频?
    华为事件启思:美国究竟有多少高科技公司?
    常用电子书下载收藏
    [置顶] 【玩转cocos2d-x之七】场景类CCScene和布景类CCLayer
    递归循环JSON
    POJ_1365_Prime_Land
    WIX在VS2012中如何制作中文安装包
    PKU Online Judge 1054:Cube (设置根节点)
    MFC——AfxParseURL用法
  • 原文地址:https://www.cnblogs.com/fatttcat/p/10147300.html
Copyright © 2011-2022 走看看