#633 · #778 · Swim in Rising Water(水位上升的泳池中游泳)

You are given an n x n grid where grid[i][j] is the elevation. Rain starts falling at time t, and you can swim to adjacent cells only when both elevations are at most t. Return the least t to swim from the top-left to the bottom-right. Constraints: 1 <= n <= 50, 0 <= grid[i][j] < n^2, all elevations are distinct.