2021-02-22：一個象棋的棋盤，而後把整個棋盤放入第一象限，棋盤的最左下角是(0,0)位置，那

2021-02-22：一個象棋的棋盤，而後把整個棋盤放入第一象限，棋盤的最左下角是(0,0)位置，那麼整個棋盤就是橫座標上9條線、縱座標上10條線的區域。給你三個 參數 x，y，k。返回「馬」從(0,0)位置出發，必須走k步。最後落在(x,y)上的方法數有多少種?
福哥答案2021-02-22：

天然智慧便可。
1.遞歸。有代碼。
2.記憶化搜索。有代碼。
3.動態規劃。dp是三維數組。棋盤是二維數組，走k步，須要k+1個棋盤。有代碼。
4.動態規劃，空間壓縮。只有相鄰棋盤纔有依賴，因此只須要用兩個棋盤，就能走完。有代碼。

代碼用golang編寫，代碼以下：

package main

import "fmt"

func main() {

    a := 3
    b := 4
    k := 5
    fmt.Println("1.遞歸：", jump1(a, b, k))
    fmt.Println("---")
    fmt.Println("2.記憶化搜索：", jump2(a, b, k))
    fmt.Println("---")
    fmt.Println("3.動態規劃：", jump3(a, b, k))
    fmt.Println("---")
    fmt.Println("4.動態規劃,空間壓縮：", jump4(a, b, k))
}

func jump1(a int, b int, k int) int {
    return process1(0, 0, k, a, b)
}
func process1(x int, y int, rest int, a int, b int) int {
    if x < 0 || x >= 9 || y < 0 || y >= 10 {
        return 0
    }
    if rest == 0 {
        if x == a && y == b {
            return 1
        } else {
            return 0
        }
    }
    ways := process1(x+2, y+1, rest-1, a, b)
    ways += process1(x+2, y-1, rest-1, a, b)
    ways += process1(x-2, y+1, rest-1, a, b)
    ways += process1(x-2, y-1, rest-1, a, b)
    ways += process1(x+1, y+2, rest-1, a, b)
    ways += process1(x+1, y-2, rest-1, a, b)
    ways += process1(x-1, y+2, rest-1, a, b)
    ways += process1(x-1, y-2, rest-1, a, b)
    return ways
}

func jump2(a int, b int, k int) int {
    dp := make([][][]int, 10)
    for i := 0; i < 10; i++ {
        dp[i] = make([][]int, 9)
        for j := 0; j < 9; j++ {
            dp[i][j] = make([]int, k+1)
            for m := 0; m < k+1; m++ {
                dp[i][j][m] = -1
            }
        }
    }
    return process2(0, 0, k, a, b, dp)
}
func process2(x int, y int, rest int, a int, b int, dp [][][]int) int {
    if x < 0 || x >= 10 {
        return 0
    }
    if y < 0 || y >= 9 {
        return 0
    }
    if dp[x][y][rest] != -1 {
        return dp[x][y][rest]
    }
    if rest == 0 {
        if x == a && y == b {
            dp[x][y][rest] = 1
            return 1
        } else {
            dp[x][y][rest] = 0
            return 0
        }
    }
    ways := process2(x+2, y+1, rest-1, a, b, dp)
    ways += process2(x+2, y-1, rest-1, a, b, dp)
    ways += process2(x-2, y+1, rest-1, a, b, dp)
    ways += process2(x-2, y-1, rest-1, a, b, dp)
    ways += process2(x+1, y+2, rest-1, a, b, dp)
    ways += process2(x+1, y-2, rest-1, a, b, dp)
    ways += process2(x-1, y+2, rest-1, a, b, dp)
    ways += process2(x-1, y-2, rest-1, a, b, dp)
    dp[x][y][rest] = ways
    return ways

}

func jump3(a int, b int, k int) int {
    dp := make([][][]int, 10)
    for i := 0; i < 10; i++ {
        dp[i] = make([][]int, 9)
        for j := 0; j < 9; j++ {
            dp[i][j] = make([]int, k+1)
        }
    }
    dp[a][b][0] = 1
    for rest := 1; rest <= k; rest++ {
        for x := 0; x < 10; x++ {
            for y := 0; y < 9; y++ {
                ways := pick3(x+2, y+1, rest-1, dp)
                ways += pick3(x+1, y+2, rest-1, dp)
                ways += pick3(x-1, y+2, rest-1, dp)
                ways += pick3(x-2, y+1, rest-1, dp)
                ways += pick3(x-2, y-1, rest-1, dp)
                ways += pick3(x-1, y-2, rest-1, dp)
                ways += pick3(x+1, y-2, rest-1, dp)
                ways += pick3(x+2, y-1, rest-1, dp)
                dp[x][y][rest] = ways
            }
        }
    }
    return dp[0][0][k]
}
func pick3(x int, y int, rest int, dp [][][]int) int {
    if x < 0 || x >= 10 || y < 0 || y >= 9 {
        return 0
    }
    return dp[x][y][rest]
}

func jump4(a int, b int, k int) int {
    dp := make([][][]int, 10)
    for i := 0; i < 10; i++ {
        dp[i] = make([][]int, 9)
        for j := 0; j < 9; j++ {
            dp[i][j] = make([]int, 2)
        }
    }
    dp[a][b][0] = 1
    for rest := 1; rest <= k; rest++ {
        for x := 0; x < 10; x++ {
            for y := 0; y < 9; y++ {
                ways := pick4(x+2, y+1, dp)
                ways += pick4(x+1, y+2, dp)
                ways += pick4(x-1, y+2, dp)
                ways += pick4(x-2, y+1, dp)
                ways += pick4(x-2, y-1, dp)
                ways += pick4(x-1, y-2, dp)
                ways += pick4(x+1, y-2, dp)
                ways += pick4(x+2, y-1, dp)
                dp[x][y][1] = ways
            }
        }
        for i := 0; i < 10; i++ {
            for j := 0; j < 9; j++ {
                dp[i][j][0], dp[i][j][1] = dp[i][j][1], 0
            }
        }
    }
    return dp[0][0][0]
}
func pick4(x int, y int, dp [][][]int) int {
    if x < 0 || x >= 10 || y < 0 || y >= 9 {
        return 0
    }
    return dp[x][y][0]
}

執行結果以下：

---

左神java代碼
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