778. Swim in Rising Water

You are given an n x n integer matrix grid where each value grid[i][j] represents the elevation at that point (i, j). It starts raining, and water gradually rises over time. At time t, the water level is t, meaning any cell with elevation less than equal to t is submerged or reachable. You can swim from a square to another 4-directionally adjacent square if and only if the elevation of both squa