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| 1 | +# 63. Unique Paths II |
| 2 | + |
| 3 | +### 2020年07月30日 |
| 4 | + |
| 5 | +A robot is located at the top-left corner of a *m* x *n* grid (marked 'Start' in the diagram below). |
| 6 | + |
| 7 | +The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below). |
| 8 | + |
| 9 | +Now consider if some obstacles are added to the grids. How many unique paths would there be? |
| 10 | + |
| 11 | + |
| 12 | + |
| 13 | +An obstacle and empty space is marked as `1` and `0` respectively in the grid. |
| 14 | + |
| 15 | +**Note:** *m* and *n* will be at most 100. |
| 16 | + |
| 17 | +**Example 1:** |
| 18 | + |
| 19 | +``` |
| 20 | +Input: |
| 21 | +[ |
| 22 | + [0,0,0], |
| 23 | + [0,1,0], |
| 24 | + [0,0,0] |
| 25 | +] |
| 26 | +Output: 2 |
| 27 | +Explanation: |
| 28 | +There is one obstacle in the middle of the 3x3 grid above. |
| 29 | +There are two ways to reach the bottom-right corner: |
| 30 | +1. Right -> Right -> Down -> Down |
| 31 | +2. Down -> Down -> Right -> Right |
| 32 | +``` |
| 33 | + |
| 34 | + |
| 35 | +# Solution |
| 36 | + |
| 37 | +```swift |
| 38 | +class Solution { |
| 39 | + |
| 40 | + func uniquePathsWithObstacles(_ obstacleGrid: [[Int]]) -> Int { |
| 41 | + let m = obstacleGrid.count |
| 42 | + guard m > 0 else { |
| 43 | + return 0 |
| 44 | + } |
| 45 | + let n = obstacleGrid[0].count |
| 46 | + guard n > 0 else { |
| 47 | + return 0 |
| 48 | + } |
| 49 | + var cache = [[Int]].init(repeating: [Int].init(repeating: 0, count: n), count: m) |
| 50 | + |
| 51 | + for y in 1...m { |
| 52 | + for x in 1...n { |
| 53 | + if obstacleGrid[y - 1][x - 1] == 1 { |
| 54 | + cache[y - 1][x - 1] = 0 |
| 55 | + } else if x == 1 { |
| 56 | + cache[y - 1][x - 1] = 1 |
| 57 | + for _y in 1...y { |
| 58 | + if obstacleGrid[_y - 1][x - 1] == 1 { |
| 59 | + cache[y - 1][x - 1] = 0 |
| 60 | + break |
| 61 | + } |
| 62 | + } |
| 63 | + } else if y == 1 { |
| 64 | + cache[y - 1][x - 1] = 1 |
| 65 | + for _x in 1...x { |
| 66 | + if obstacleGrid[y - 1][_x - 1] == 1 { |
| 67 | + cache[y - 1][x - 1] = 0 |
| 68 | + break |
| 69 | + } |
| 70 | + } |
| 71 | + } else { |
| 72 | + cache[y - 1][x - 1] = cache[y - 2][x - 1] + cache[y - 1][x - 2] |
| 73 | + } |
| 74 | + } |
| 75 | + } |
| 76 | + return cache[m - 1][n - 1] |
| 77 | + } |
| 78 | +} |
| 79 | + |
| 80 | +``` |
| 81 | + |
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