#602 · #1219 · Path with Maximum Gold(黄金矿工)

In a gold mine grid, each cell holds a non-negative amount of gold; 0 means an obstacle. Starting anywhere, you may move in the four cardinal directions but cannot revisit a cell, and cannot enter a 0. Return the maximum gold you can collect. Constraints: 1 <= m, n <= 15, 0 <= grid[i][j] <= 100.