<pre class="shiki github-dark shaku"><code>/** * @param {string} str * @return {string} */function smallestUniqueSubstr(str) { const lastIndex = {} for (let i = 0; i &lt; str.length; i++) { lastIndex[str[i]] = i } const stack = [] const seen = new Set() for (let i = 0; i &lt; str.length; i++) { const char = str[i] if (seen.has(char)) { continue } while (stack.length &amp;&amp; char &lt; stack[stack.length - 1] &amp;&amp; i &lt; lastIndex[stack[stack.length - 1]]) { seen.delete(stack.pop()) } stack.push(char) seen.add(char) } return stack.join('')}</code></pre>

This is my accepted solution.

Given a string, write a function to remove the duplicate characters to make sure that each character only occurs once. For example 'xyzabcxyzabc' Each…