Merge pull request #2021 from tahsintunan/778

Create 778. Swim in Rising Water

Author: tahsintunan

go/0778-swim-in-rising-water.go

@@ -0,0 +1,52 @@
+var dirs = []int{0, 1, 0, -1, 0}
+
+func swimInWater(grid [][]int) int {
+	gridSize := len(grid)
+	minTime, maxTime := grid[0][0], gridSize*gridSize-1
+
+	for minTime < maxTime {
+		middleTime := minTime + (maxTime-minTime)/2
+		visited := initVisitedArray(gridSize)
+		if canReach(grid, visited, 0, 0, gridSize, middleTime) {
+			maxTime = middleTime
+		} else {
+			minTime = middleTime + 1
+		}
+	}
+	return minTime
+}
+
+func initVisitedArray(gridSize int) [][]bool {
+	visited := make([][]bool, gridSize)
+	for i := range visited {
+		visited[i] = make([]bool, gridSize)
+	}
+	return visited
+}
+
+func canReach(grid [][]int, visited [][]bool, x, y, gridSize, level int) bool {
+	visited[x][y] = true
+	for i := 0; i < 4; i++ {
+		newX, newY := x+dirs[i], y+dirs[i+1]
+		if !isValidMove(newX, newY, gridSize) {
+			continue
+		}
+		if visited[newX][newY] || grid[newX][newY] > level {
+			continue
+		}
+		if newX == gridSize-1 && newY == gridSize-1 {
+			return true
+		}
+		if canReach(grid, visited, newX, newY, gridSize, level) {
+			return true
+		}
+	}
+	return false
+}
+
+func isValidMove(x, y, gridSize int) bool {
+	if y < 0 || x < 0 || y >= gridSize || x >= gridSize {
+		return false
+	}
+	return true
+}