@[AveryJH](/user/979902)
你这个特判的地方有些问题。
首先是step函数里第一个判断是否到达A点时应该是x和y同时为0才能赋值成1，还有就是你的数组开小了，题目是 n,m <= 20，但是数组的编号是从0开始排序的，所以你要用到第20位，就至少要开到memory[21][21]
```cpp
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
using namespace std;
//存储已知路径数
long long int memory[21][21];
long long int step(int x1 ,int y1 , int x2 ,int y2 ){
if(x1 == 0 && y1 == 0){
memory[x1][y1]=1;
return 1;
}
//马的看守范围
else if(abs(x2-x1)+abs(y2-y1)==3 && x1!=x2 &&y1!=y2){
memory[x1][y1]=0;
return 0;
}
//马的位置
else if(x1==x2&&y1==y2){
memory[x1][y1]=0;
return 0;
}
if(memory[x1][y1] != -1){
return memory[x1][y1];
}
long long int result;
if(x1 - 1 >= 0 && y1 - 1 >= 0)
result = step(x1-1,y1,x2,y2)+step(x1,y1-1,x2,y2);
else if(x1 - 1 >= 0 && y1 - 1 < 0)
result = step(x1-1,y1,x2,y2);
else if(x1 - 1 < 0 && y1 - 1 >= 0)
result = step(x1,y1-1,x2,y2);
memory[x1][y1]=result;
return result;
}
int main(){
int a,b,c,d;
cin>>a>>b>>c>>d;
//a,b b pos
//c,d ma pos
//初始化二维数组
memset(memory,-1,sizeof memory);
//cout<<a<<b<<c<<d<<endl;
cout<<step(a,b,c,d)<<endl;
return 0;
}
```
by calm_alone @ 2023-03-28 18:20:55
```cpp
#include <cmath>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#define ll long long
inline int read(){
int num = 0; char c = getchar();
while(!isdigit(c)) c = getchar();
while(isdigit(c)) num = (num << 1) + (num << 3) + (c ^ '0'), c = getchar();
return num;
}
int bx, by, mx, my;
ll f[30];
inline bool check(int x, int y) {
if(x == mx && y == my) return 1;
return (std::abs(mx - x) + std::abs(my - y) == 3) && (std::max ((std::abs(mx - x)), std::abs(my - y)) == 2);
}
int main(){
bx = read() + 2, by = read() + 2, mx = read() + 2, my = read() + 2;
f[2] = 1;
for(int i = 2; i <= bx; i++){
for(int j = 2; j <= by; j++){
if(check(i, j)){
f[j] = 0;
continue;
}
f[j] += f[j - 1];
}
}
printf("%lld\n", f[by]);
return 0;
}
```
by lihaoyu9889 @ 2023-03-31 19:56:02