<p>You are given an array <code>happiness</code> of length <code>n</code>, and a <strong>positive</strong> integer <code>k</code>.</p> <p>There are <code>n</code> children standing in a queue, where the <code>i<sup>th</sup></code> child has <strong>happiness value</strong> <code>happiness[i]</code>. You want to select <code>k</code> children from these <code>n</code> children in <code>k</code> turns.</p> <p>In each turn, when you select a child, the <strong>happiness value</strong> of all the children that have <strong>not</strong> been selected till now decreases by <code>1</code>. Note that the happiness value <strong>cannot</strong> become negative and gets decremented <strong>only</strong> if it is positive.</p> <p>Return <em>the <strong>maximum</strong> sum of the happiness values of the selected children you can achieve by selecting </em><code>k</code> <em>children</em>.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input:</strong> happiness = [1,2,3], k = 2 <strong>Output:</strong> 4 <strong>Explanation:</strong> We can pick 2 children in the following way: - Pick the child with the happiness value == 3. The happiness value of the remaining children becomes [0,1]. - Pick the child with the happiness value == 1. The happiness value of the remaining child becomes [0]. Note that the happiness value cannot become less than 0. The sum of the happiness values of the selected children is 3 + 1 = 4. </pre> <p><strong class="example">Example 2:</strong></p> <pre> <strong>Input:</strong> happiness = [1,1,1,1], k = 2 <strong>Output:</strong> 1 <strong>Explanation:</strong> We can pick 2 children in the following way: - Pick any child with the happiness value == 1. The happiness value of the remaining children becomes [0,0,0]. - Pick the child with the happiness value == 0. The happiness value of the remaining child becomes [0,0]. The sum of the happiness values of the selected children is 1 + 0 = 1. </pre> <p><strong class="example">Example 3:</strong></p> <pre> <strong>Input:</strong> happiness = [2,3,4,5], k = 1 <strong>Output:</strong> 5 <strong>Explanation:</strong> We can pick 1 child in the following way: - Pick the child with the happiness value == 5. The happiness value of the remaining children becomes [1,2,3]. The sum of the happiness values of the selected children is 5. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= n == happiness.length <= 2 * 10<sup>5</sup></code></li> <li><code>1 <= happiness[i] <= 10<sup>8</sup></code></li> <li><code>1 <= k <= n</code></li> </ul>