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[Swift]LeetCode85. 最大矩形 | Maximal Rectangle

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Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.

Example:

Input:
[
  ["1","0","1","0","0"],
  ["1","0","1","1","1"],
  ["1","1","1","1","1"],
  ["1","0","0","1","0"]
]
Output: 6

给定一个仅包含 0 和 1 的二维二进制矩阵，找出只包含 1 的最大矩形，并返回其面积。

示例:

输入:
[
  ["1","0","1","0","0"],
  ["1","0","1","1","1"],
  ["1","1","1","1","1"],
  ["1","0","0","1","0"]
]
输出: 6
160ms
 1 class Solution {
 2     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 3         if matrix.count == 0 || matrix[0].count == 0{
 4             return 0
 5         }
 6         var ans = 0
 7         var rowArr = Array(repeating:0,count:matrix[0].count + 1)
 8         for y in stride(from:0,to:matrix.count,by:1) {
 9             for x in stride(from:0,to:matrix[0].count,by:1) {
10                 if matrix[y][x] == "1" {
11                     rowArr[x] += 1 
12                 } else {
13                     rowArr[x] = 0
14                 }
15             }
16             ans = max(ans,getLargetRect(rowArr))
17         }
18         return ans
19     }
20     
21     func getLargetRect(_ rowArr:[Int]) -> Int {
22         var stack = [Int]()
23         var maxArea = 0
24         for (index,height) in rowArr.enumerated() {
25             while let last = stack.last, rowArr[last] > height {
26                 stack.removeLast()
27                 var width = 0
28                 if stack.isEmpty {
29                     width = index
30                 } else {
31                     width = index - stack.last! - 1
32                 }
33                 maxArea = max(maxArea, width * rowArr[last] )
34             }
35 
36             stack.append(index)
37         }
38         return maxArea
39     }
40 }

168ms

 1 class Solution {
 2     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 3         let n = matrix.count
 4         guard n > 0 else {
 5             return 0
 6         }
 7         let m = matrix[0].count
 8         
 9         var mark = Array(repeatElement(Array(repeatElement(0, count: m)), count: n))
10         for i in (0..<n).reversed() {
11             var count = 0
12             for j in (0..<m).reversed() {
13                 if matrix[i][j] == "1" {
14                     count += 1
15                 } else {
16                     count = 0
17                 }
18                 mark[i][j] = count
19             }
20         }
21 
22         var result = 0
23         for i in 0..<n {
24             for j in 0..<m {
25                 var minColumn = m
26                 var row = i
27                 while row < n && mark[row][j] != 0 {
28                     minColumn = min(minColumn, mark[row][j])
29                     result = max(result, (row - i + 1) * minColumn)
30                     row += 1
31                 }
32             }
33         }
34         return result
35     }
36 }

200ms

 1 class Solution {
 2 
 3     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 4         
 5         if matrix.count == 0 || matrix[0].count == 0 {
 6             return 0
 7         }
 8         
 9         var heights = [Int](repeating: 0, count: matrix[0].count)
10         var s = 0
11         
12         for i in 0..<matrix.count {
13             
14             for j in 0..<matrix[i].count {
15                 
16                 if matrix[i][j] == "1" {
17                     
18                     heights[j] += 1
19                     
20                 } else {
21                     heights[j] = 0
22                 }
23             }
24             
25             s = max(s, largestRectangleArea(heights))
26         }
27         
28         return s
29     }
30     
31     func largestRectangleArea(_ heights: [Int]) -> Int {
32         
33         if heights.count == 0 {
34             return 0
35         }
36         
37         var myHeights: [Int] = heights
38         myHeights.append(0)
39         
40         
41         var s = 0
42         //swift中没有栈,使用数组代替,永远操作最后一位
43         var stack: [Int] = []
44         var i = 0
45         
46         while i < myHeights.count {
47             
48             if stack.count == 0 || myHeights[stack.last!] < myHeights[i] {
49                 
50                 stack.append(i)
51                 i += 1
52             } else {
53                 
54                 let j = stack.last!
55                 stack.removeLast()
56                 
57                 //如果栈为空,说明数组第一位即构成矩形的左侧边界,此时索引大小即矩形长度
58                 //如果不为空,用栈顶索引和当前索引计算矩形长度
59                 s = max(s, myHeights[j]*(stack.isEmpty ? i : i - 1 - stack.last!))
60             }
61         }
62         return s
63     }
64         
65 }

416ms

 1 class Solution {
 2     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 3         guard matrix.count > 0 && matrix[0].count > 0 else {
 4             return 0
 5         }
 6         let m = matrix.count
 7         let n = matrix[0].count
 8         var left = [Int](repeating: 0, count: n)
 9         var right = [Int](repeating: n, count: n)
10         var height = [Int](repeating: 0, count: n)
11         var result = 0
12         for i in 0..<m {
13             var currentLeft = 0
14             var currentRight = n
15             for j in 0..<n {
16                 if (matrix[i][j] == "1") {
17                     left[j] = max(left[j], currentLeft)
18                     height[j] = height[j] + 1
19                 } else {
20                     left[j] = 0
21                     currentLeft = j + 1
22                     height[j] = 0
23                 }
24                 if (matrix[i][n - j - 1] == "1") {
25                     right[n - j - 1] = min(right[n - j - 1], currentRight)
26                 } else {
27                     currentRight = n - j - 1
28                     right[n - j - 1] = n
29                 }
30             }
31             for j in 0..<n {
32                 result = max(result, (right[j] - left[j]) * height[j])
33             }
34         }
35         return result
36     }
37 }

436ms

 1 class HistoArea {
 2     func largestRectangleArea(_ heights: [Int]) -> Int {
 3         var stack = [Int]()
 4         var max = 0
 5         for i in 0..<heights.count {
 6             if stack.count == 0 || heights[i]>=heights[stack[stack.count-1]] {
 7                 stack.append(i)
 8             } else {
 9                 while stack.count > 0 && heights[i] < heights[stack[stack.count-1]] {
10                     let area = eval(&stack, heights, i)
11                     if area > max {
12                         max = area
13                     }
14                 }
15                 stack.append(i)
16             }
17         }
18         while stack.count > 0 {
19             let area = eval(&stack, heights, heights.count)
20             if area > max {
21                 max = area
22             }
23         }
24         return max
25     }
26     
27     func eval(_ stack: inout [Int], _ heights: [Int], _ end: Int) -> Int {
28         let idx = stack.last!
29         stack.removeLast()
30         var area = 0
31 
32         if let start = stack.last {
33             area = heights[idx]*(end-start-1)
34         } else {
35             area = heights[idx]*end
36         }
37         return area
38     }
39 }
40 
41 class Solution {
42     func maximalRectangle(_ matrix: [[Character]]) -> Int {
43         let hist = HistoArea()
44         var histogram = [Int]()
45         if matrix.count == 0 {
46             return 0
47         }
48         for i in 0..<matrix[0].count {
49             histogram.append(0)
50         }
51         var maxArea = 0
52         
53         for i in 0..<matrix.count {
54             for j in 0..<matrix[0].count {
55                 if matrix[i][j] == "1" {
56                     histogram[j] += 1
57                 } else {
58                     histogram[j] = 0
59                 }
60             }
61             let area = hist.largestRectangleArea(histogram)
62             if area > maxArea {
63                 maxArea = area
64             }
65         }
66         return maxArea
67     }
68 }

452ms

 1 class Solution {
 2     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 3         if matrix.count == 0 || matrix[0].count == 0 {
 4             return 0
 5         }
 6 
 7         let rLen = matrix.count
 8         let cLen = matrix[0].count
 9         var h = [Int](repeating: 0, count: cLen + 1)
10         var maxValue = 0
11 
12         for row in 0..<rLen {
13             var stack = [Int]()
14             for i in 0..<(cLen + 1) {
15                 if i < cLen {
16                     if matrix[row][i] == "1" {
17                         h[i] += 1
18                     } else {
19                         h[i] = 0
20                     }
21                 }
22                 if stack.isEmpty || h[stack.last!] <= h[i] {
23                     stack.append(i)
24                 } else {
25                     while !stack.isEmpty && h[i] < h[stack.last!] {
26                         let top = stack.removeLast()
27                         let area = h[top] * (stack.isEmpty ? i : (i - stack.last! - 1))
28                         if area > maxValue {
29                             maxValue = area
30                         }
31                     }
32                     stack.append(i)
33                 }
34             }
35         }
36         return maxValue
37     }
38 }

588ms

 1 class Solution {
 2     func maximalRectangle(_ matrix: [[Character]]) -> Int {
 3         let n = matrix.count
 4         guard n > 0 else {
 5             return 0
 6         }
 7         let m = matrix[0].count
 8         
 9         var mark = Array(repeatElement(Array(repeatElement(0, count: m)), count: n))
10         for i in (0..<n).reversed() {
11             var count = 0
12             for j in (0..<m).reversed() {
13                 if matrix[i][j] == "1" {
14                     count += 1
15                 } else {
16                     count = 0
17                 }
18                 mark[i][j] = count
19             }
20         }
21 
22         var result = 0
23         for i in 0..<n {
24             for j in 0..<m {
25                 var minColumn = m
26                 var row = i
27                 while row < n && mark[row][j] != 0 {
28                     minColumn = min(minColumn, mark[row][j])
29                     result = max(result, (row - i + 1) * minColumn)
30                     row += 1
31                 }
32             }
33         }
34         return result
35     }
36 }

 

posted @ 2018-11-09 15:55  为敢技术  阅读(415)  评论(0)  编辑  收藏  举报