Package g0501_0600.s0519_random_flip_matrix

Class Solution

java.lang.Object
g0501_0600.s0519_random_flip_matrix.Solution
public class Solution extends Object
519 - Random Flip Matrix.<p>Medium</p> <p>There is an <code>m x n</code> binary grid <code>matrix</code> with all the values set <code>0</code> initially. Design an algorithm to randomly pick an index <code>(i, j)</code> where <code>matrix[i][j] == 0</code> and flips it to <code>1</code>. All the indices <code>(i, j)</code> where <code>matrix[i][j] == 0</code> should be equally likely to be returned.</p> <p>Optimize your algorithm to minimize the number of calls made to the <strong>built-in</strong> random function of your language and optimize the time and space complexity.</p> <p>Implement the <code>Solution</code> class:</p> <ul> <li><code>Solution(int m, int n)</code> Initializes the object with the size of the binary matrix <code>m</code> and <code>n</code>.</li> <li><code>int[] flip()</code> Returns a random index <code>[i, j]</code> of the matrix where <code>matrix[i][j] == 0</code> and flips it to <code>1</code>.</li> <li><code>void reset()</code> Resets all the values of the matrix to be <code>0</code>.</li> </ul> <p><strong>Example 1:</strong></p> <p><strong>Input</strong> [&ldquo;Solution&rdquo;, &ldquo;flip&rdquo;, &ldquo;flip&rdquo;, &ldquo;flip&rdquo;, &ldquo;reset&rdquo;, &ldquo;flip&rdquo;] [[3, 1], [], [], [], [], []]</p> <p><strong>Output:</strong> [null, [1, 0], [2, 0], [0, 0], null, [2, 0]]</p> <p><strong>Explanation:</strong> Solution solution = new Solution(3, 1); solution.flip(); // return [1, 0], [0,0], [1,0], and [2,0] should be equally likely to be returned. solution.flip(); // return [2, 0], Since [1,0] was returned, [2,0] and [0,0] solution.flip(); // return [0, 0], Based on the previously returned indices, only [0,0] can be returned. solution.reset(); // All the values are reset to 0 and can be returned. solution.flip(); // return [2, 0], [0,0], [1,0], and [2,0] should be equally likely to be returned.</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= m, n <= 10<sup>4</sup></code></li> <li>There will be at least one free cell for each call to <code>flip</code>.</li> <li>At most <code>1000</code> calls will be made to <code>flip</code> and <code>reset</code>.</li> </ul>

  • Constructor Details

    • Solution

      public Solution(int nRows, int nCols)

  • Method Details

    • flip

      public int[] flip()

    • reset

      public void reset()