Number of Days in a Month
<p>Given a year <code>year</code> and a month <code>month</code>, return <em>the number of days of that month</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> year = 1992, month = 7
<strong>Output:</strong> 31
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> year = 2000, month = 2
<strong>Output:</strong> 29
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> year = 1900, month = 2
<strong>Output:</strong> 28
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1583 &lt;= year &lt;= 2100</code></li>
	<li><code>1 &lt;= month &lt;= 12</code></li>
</ul>
Math
class Solution {
    public int numberOfDays(int year, int month) {
        boolean leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
        int[] days = new int[] {0, 31, leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
        return days[month];
    }
}