<pre class="shiki github-dark shaku"><code>/** * @param {number[]} arr - ascending array with duplicates * @param {number} target * @return {number} */function lastIndex(arr, target){ // your code here let left = 0; right = arr.length - 1; while(left &lt; right) { let mid = left + Math.floor((right - left) / 2); if(arr[mid] &gt; target) { right = mid; } else { left = mid + 1; } } if (arr[left] === target) { return left; } if (left - 1 &amp;&amp; arr[left - 1] === target) { return left - 1; } return -1;}console.log(lastIndex([1,2,3,4,4,4,4, 100, 1000, 10000], 4))console.log(lastIndex([1,2,3,4,4,4,4, 1000, 10000], 4))console.log(lastIndex([1,2,3,4,4,4,4, 10000], 4))console.log(lastIndex([1,2,3,4,4,4,4], -1))console.log(lastIndex([1,2,3,4,4,4,4], 4))console.log(lastIndex([1,2,3,4,4,4,4], 5))console.log(lastIndex([1,1, 1, 1], 1))console.log(lastIndex([1,1, 1], 1))console.log(lastIndex([1,1], 1))console.log(lastIndex([1], 1))console.log(lastIndex([], 1))</code></pre>

Binary search. Similar template with a little tweak.

This is a variation of 37. implement Binary Search (unique). Your are given a sorted ascending array of number, but might have duplicates, you are ask…