<p>Given an integer array <code>nums</code> with possible <strong>duplicates</strong>, randomly output the index of a given <code>target</code> number. You can assume that the given target number must exist in the array.</p> <p>Implement the <code>Solution</code> class:</p> <ul> <li><code>Solution(int[] nums)</code> Initializes the object with the array <code>nums</code>.</li> <li><code>int pick(int target)</code> Picks a random index <code>i</code> from <code>nums</code> where <code>nums[i] == target</code>. If there are multiple valid i's, then each index should have an equal probability of returning.</li> </ul> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre> <strong>Input</strong> ["Solution", "pick", "pick", "pick"] [[[1, 2, 3, 3, 3]], [3], [1], [3]] <strong>Output</strong> [null, 4, 0, 2] <strong>Explanation</strong> Solution solution = new Solution([1, 2, 3, 3, 3]); solution.pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning. solution.pick(1); // It should return 0. Since in the array only nums[0] is equal to 1. solution.pick(3); // It should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning. </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= nums.length <= 2 * 10<sup>4</sup></code></li> <li><code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code></li> <li><code>target</code> is an integer from <code>nums</code>.</li> <li>At most <code>10<sup>4</sup></code> calls will be made to <code>pick</code>.</li> </ul>