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  • Google资深工程师深度讲解Go语言迷宫的广度优先搜索(十二)

    一.广度优先算法

    • 为爬虫实战项目做好准备
    • 应用广泛,综合性强
    • 面试常见

    探索顺序: 上左下右

    节点三种状态:

    1. 已经发现,但没有探索过 
    2. 已经发现,并探索完成
    3. 没有发现

    结束条件:(1)走到终点  (2)走到队列为空

    maze.go读取文件

    package main
    
    import (
    	"fmt"
    	"os"
    )
    
    func readMaze(filename string) [][]int {
    	file, err := os.Open(filename)
    	if err != nil {
    		panic(err)
    	}
    
    	var row, col  int
    	fmt.Fscanf(file, "%d %d", &row, &col)
    
    	maze := make([][]int, row)
    	for i := range maze {
    		maze[i] = make([]int, col)
    		for j := range maze[i] {
    			fmt.Fscanf(file, "%d", &maze[i][j])
    		}
    	}
    	return maze
    
    }
    
    func main() {
    	maze:=readMaze("maze/maze.in")
    	for _,row:= range maze{
    		for _,val:=range row {
    			fmt.Printf("%d ",val)
    		}
    		fmt.Println()
    	}
    }
    

    maze.in文件

    6 5
    0 1 0 0 0
    0 0 0 1 0
    0 1 0 1 0
    1 1 1 0 0
    0 1 0 0 1
    0 1 0 0 0

    广度优先算法代码

    package main
    
    import (
    	"fmt"
    	"os"
    )
    
    type point struct {
    	i, j int
    }
    
    var dirs = [4]point{
    	{-1, 0}, {0, -1}, {1, 0}, {0, 1}}
    
    func (p point) add(r point) point {
    	return point{p.i + r.i, p.j + r.j}
    }
    
    func (p point) at(grid [][]int) (int, bool) {
    	if p.i < 0 || p.i >= len(grid) {
    		return 0, false
    	}
    	if p.j < 0 || p.j >= len(grid[p.i]) {
    		return 0, false
    	}
    	return grid[p.i][p.j], true
    }
    
    func walk(maze [][]int, start, end point)[][]int {
    	steps := make([][]int, len(maze))
    	for i := range steps {
    		steps[i] = make([]int, len(maze[i]))
    	}
    
    	//队列
    	Q := []point{start}
    	for len(Q) > 0 {
    		cur := Q[0]
    		Q = Q[1:]
    
    		if cur==end {
    			break
    		}
    
    		for _, dir := range dirs {
    			next := cur.add(dir)
    
    			//maze at next is 0
    			//and steps at next is 0
    			//and next !=start
    			val, ok := next.at(maze)
    			if !ok || val == 1 {
    				continue
    			}
    			val, ok = next.at(steps)
    			if !ok || val != 0 {
    				continue
    			}
    			if next == start {
    				continue
    			}
    
    			curSteps, _ := cur.at(steps)
    			steps[next.i][next.j] = curSteps + 1
    			Q = append(Q, next)
    		}
    	}
    	return steps
    }
    func readMaze(filename string) [][]int {
    	file, err := os.Open(filename)
    	if err != nil {
    		panic(err)
    	}
    
    	var row, col int
    	fmt.Fscanf(file, "%d %d", &row, &col)
    
    	maze := make([][]int, row)
    	for i := range maze {
    		maze[i] = make([]int, col)
    		for j := range maze[i] {
    			fmt.Fscanf(file, "%d", &maze[i][j])
    		}
    	}
    	return maze
    }
    
    func main() {
    	maze := readMaze("maze/maze.in")
    	/*for _, row := range maze {
    		for _, val := range row {
    			fmt.Printf("%d ", val)
    		}
    		fmt.Println()
    	}*/
    
    	steps:=walk(maze, point{0, 0}, point{len(maze) - 1, len(maze[0]) - 1})
    	for _,row:=range steps {
    		for _,val:=range row{
    			fmt.Printf("%3d",val)
    		}
    		fmt.Println()
    	}
    }
    

    结果:

    总结

    • 用循环创建二维slice
    • 使用slice来实现队列
    • 用Fscanf读取文件
    • 对point的抽象

    赞赏码

    非学,无以致疑;非问,无以广识

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  • 原文地址:https://www.cnblogs.com/lxwphp/p/15452716.html
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