count-substrings-starting-and-ending-with-given-character

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Algorithms

You are given a string <code>s</code> and a character <code>c</code>. Return the total number of substrings of <code>s</code> that start and end with <code>c</code>.

&nbsp;
Example 1:

<div class="example-block" style="border-color: var(--border-tertiary); border-left-width: 2px; color: var(--text-secondary); font-size: .875rem; margin-bottom: 1rem; margin-top: 1rem; overflow: visible; padding-left: 1rem;">
Input: s = &quot;abada&quot;, c = &quot;a&quot;

Output: 6

Explanation: Substrings starting and ending with <code>&quot;a&quot;</code> are: <code>&quot;abada&quot;</code>, <code>&quot;abada&quot;</code>, <code>&quot;abada&quot;</code>, <code>&quot;abada&quot;</code>, <code>&quot;abada&quot;</code>, <code>&quot;abada&quot;</code>.
</div>

Example 2:

<div class="example-block" style="border-color: var(--border-tertiary); border-left-width: 2px; color: var(--text-secondary); font-size: .875rem; margin-bottom: 1rem; margin-top: 1rem; overflow: visible; padding-left: 1rem;">
Input: s = &quot;zzz&quot;, c = &quot;z&quot;

Output: 6

Explanation: There are a total of <code>6</code> substrings in <code>s</code> and all start and end with <code>&quot;z&quot;</code>.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code> and <code>c</code> consist&nbsp;only of lowercase English letters.</li>
</ul>

countSubstrings

Count Substrings Starting and Ending with Given Character

Math

String

Counting

给你一个字符串 <code>s</code> 和一个字符 <code>c </code>。返回在字符串 <code>s</code> 中并且以 <code>c</code> 字符开头和结尾的非空子字符串的总数。

&nbsp;

示例 1：

<div class="example-block" style="border-color: var(--border-tertiary); border-left-width: 2px; color: var(--text-secondary); font-size: .875rem; margin-bottom: 1rem; margin-top: 1rem; overflow: visible; padding-left: 1rem;">
输入：s = "abada", c = "a"

输出：6

解释：以 <code>"a"</code> 开头和结尾的子字符串有： <code>"abada"</code>、<code>"abada"</code>、<code>"abada"</code>、<code>"abada"</code>、<code>"abada"</code>、<code>"abada"</code>。
</div>

示例 2：

<div class="example-block" style="border-color: var(--border-tertiary); border-left-width: 2px; color: var(--text-secondary); font-size: .875rem; margin-bottom: 1rem; margin-top: 1rem; overflow: visible; padding-left: 1rem;">
输入：s = "zzz", c = "z"

输出：6

解释：字符串 <code>s</code> 中总共有 <code>6</code> 个子字符串，并且它们都以 <code>"z"</code> 开头和结尾。
</div>

&nbsp;

提示：

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code> 和 <code>c</code> 均由小写英文字母组成。</li>
</ul>