1631. Path With Minimum Effort

Author: partho-maple

README.md

@@ -616,8 +616,9 @@ BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spa
 |47| [1245. Tree Diameter](https://tinyurl.com/yxq4uykv) | [Python](https://tinyurl.com/wu6rdaw/1245_Tree_Diameter.py), [Swift](https://tinyurl.com/wuja3c4/1245_Tree_Diameter.swift) | [Art 1](https://www.geeksforgeeks.org/longest-path-undirected-tree/) | Medium |📌 Learned, 2 BFS. Important and interesting |
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 |49| [286. Walls and Gates](https://tinyurl.com/y3ollzsl) | [Python](https://tinyurl.com/wu6rdaw/286_Walls_and_Gates.py), [Swift](https://tinyurl.com/wuja3c4/286_Walls_and_Gates.swift) | --- | Medium |📌 BFS, DFS |
-|50| [286. Walls and Gates](https://tinyurl.com/y2xk6r98) | [Python](https://tinyurl.com/wu6rdaw/1138_Alphabet_Board_Path.py), [Swift](https://tinyurl.com/wuja3c4/1138_Alphabet_Board_Path.swift) | --- | Medium |📌 BFS |
+|50| [1138. Alphabet Board Path](https://tinyurl.com/y2xk6r98) | [Python](https://tinyurl.com/wu6rdaw/1138_Alphabet_Board_Path.py), [Swift](https://tinyurl.com/wuja3c4/1138_Alphabet_Board_Path.swift) | --- | Medium |📌 BFS |
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+|52| **[1631. Path With Minimum Effort](https://tinyurl.com/y3nh25d9) **| [Python](https://tinyurl.com/wu6rdaw/1631_Path_With_Minimum_Effort.py), [Swift](https://tinyurl.com/wuja3c4/1631_Path_With_Minimum_Effort.swift) | --- | Medium |📌 BFS, DFS, Binary search |
 
 
 </p>

leetcode.com/swift/DS_ALGO_PRAC.playground/Contents.swift

@@ -4,19 +4,42 @@ class Solution {
         guard !heights.isEmpty, !heights[0].isEmpty else {
             return 0
         }
-        var heights = heights
-        var minEffort = heights[0][0]
-        var queue = Array([0,0])
-        while !queue.isEmpty {
-            var currentCell = queue.removeFirst()
-            var (currentX, currentY) = (currentCell[0], currentCell[1])
-            var currentMinEffort = heights[currentX][currentY]
-            var currentLevelSize = queue.count
-            
-            for _ in 0..<currentLevelSize {
+        
+        var visited = Set<String>()
+        visited.insert("0-0")
+        var (path, minPath) = ([heights[0][0]], heights[0][0])
+        
+        minimumEffortPathDFSHelper(heights, path, &minPath, 0, 0, &visited)
+        return minPath
+    }
+    
+    func minimumEffortPathDFSHelper(_ heights: [[Int]], _ path: [Int], _ minPath: inout Int, _ currentX: Int, _ currentY: Int, _ visited: inout Set<String>) {
+        print("currentX: \(currentX), currentY: \(currentY)")
+        if currentX == heights.count - 1 && currentY == heights[0].count - 1 {
+            minPath = min(minPath, path.max()!)
+            print("path: \(path)")
+            return
+        }
+        print("------")
+        for neighbor in [(-1,0),(0,1),(1,0),(0,-1)] {
+            var (newX, newY) = (currentX + neighbor.0, currentY + neighbor.1)
+            if newX >= 0 && newX < heights.count && newY >= 0 && newY < heights[newX].count && !visited.contains("\(newX)-\(newY)") {
+                var currVal = heights[newX][newY]
+                var prevVal = heights[currentX][currentY]
 
+                visited.insert("\(newX)-\(newY)")
+                minimumEffortPathDFSHelper(heights, path + [abs(prevVal - currVal)], &minPath, newX, newY, &visited)
+                visited.remove("\(newX)-\(newY)")
             }
-            minEffort = max(minEffort, currentMinEffort)
         }
     }
 }
+
+/*
+ [
+ [1,2,1,1,1],
+ [1,2,1,2,1],
+ [1,2,1,2,1],
+ [1,2,1,2,1],
+ [1,1,1,2,1]]
+ */

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/1631_Path_With_Minimum_Effort.swift

@@ -0,0 +1,37 @@
+import Foundation
+
+// Simple DFS. TLE
+class Solution {
+    func minimumEffortPath(_ heights: [[Int]]) -> Int {
+        guard !heights.isEmpty, !heights[0].isEmpty else {
+            return 0
+        }
+        
+        var visited = Set<String>()
+        visited.insert("0-0")
+        var (path, minPath) = ([0], Int.max)
+        
+        minimumEffortPathDFSHelper(heights, path, &minPath, 0, 0, &visited)
+        return minPath
+    }
+    
+    func minimumEffortPathDFSHelper(_ heights: [[Int]], _ path: [Int], _ minPath: inout Int, _ currentX: Int, _ currentY: Int, _ visited: inout Set<String>) {
+        if currentX == heights.count - 1 && currentY == heights[0].count - 1 {
+            minPath = min(minPath, path.max()!)
+            return
+        }
+        for neighbor in [(-1,0),(0,1),(1,0),(0,-1)] {
+            var (newX, newY) = (currentX + neighbor.0, currentY + neighbor.1)
+            if newX >= 0 && newX < heights.count && newY >= 0 && newY < heights[newX].count && !visited.contains("\(newX)-\(newY)") {
+                var currVal = heights[newX][newY]
+                var prevVal = heights[currentX][currentY]
+                let diff = abs(prevVal - currVal)
+                if diff < minPath {
+                    visited.insert("\(newX)-\(newY)")
+                    minimumEffortPathDFSHelper(heights, path + [diff], &minPath, newX, newY, &visited)
+                    visited.remove("\(newX)-\(newY)")
+                }
+            }
+        }
+    }
+}