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