[数据结构与算法]1342. 将数字变成 0 的操作次数 / 1507. 转变日期格式

1342. 将数字变成 0 的操作次数【简单题】【每日一题】

思路：【模拟】

1. 定义计数变量ans=0；
2. 当num>0时，如果num是偶数，就将其除2，如果是奇数，就将其减1；每次操作ans加1。
3. 最后返回ans。

代码：

class Solution {
    public int numberOfSteps(int num) {
        int ans = 0;
        while (num>0){
            if (num % 2 == 0){
                num /= 2;
            }else {
                num--;
            }
            ans++;
        }
        return ans;
    }
}

1507. 转变日期格式

思路：【打表】

1. 打表直接冲就完了。

代码：

class Solution {
    public String reformatDate(String date) {
        String[] days = {"1st","2nd","3rd","4th","5th","6th","7th","8th","9th","10th","11th","12th","13th","14th","15th","16th","17th","18th","19th","20th","21st","22nd","23rd","24th","25th","26th","27th","28th","29th","30th","31st"};
        Map<String ,String > months = new HashMap<String ,String >(){
            {
                put("Jan","01");
                put("Feb","02");
                put("Mar","03");
                put("Apr","04");
                put("May","05");
                put("Jun","06");
                put("Jul","07");
                put("Aug","08");
                put("Sep","09");
                put("Oct","10");
                put("Nov","11");
                put("Dec","12");
            }
        };
        StringBuilder sb = new StringBuilder();
        String[] split = date.split(" ");
        sb.append(split[2]);
        sb.append("-");
        sb.append(months.get(split[1]));
        sb.append("-");
        for (int i = 0; i < 31; i++) {
            if (split[0].equals(days[i])){
                if (i<9){
                    sb.append("0");
                }
                sb.append(i+1);
                break;
            }
        }
        return sb.toString();
    }
}

用时对比：

农历2021最后一天，除夕快乐，新年快乐！