【dfs套dfs套dfs】算24点

 Luogu P1236 算24点

值得纪念一下

#include<cstdio>
#include<iostream>
#define ri register int
#define ll long long
using namespace std;
int a, b, c, d;
int ans[20];
char s[5];
bool flag = 0;
bool dfs3(int x, int y) {
    if(x < y) swap(x, y);
    if(x + y == 24) {
        ans[1] = x, ans[2] = y;
        s[1] = '+';
        return true;
    }
    else if(x - y == 24) {
        ans[1] = x, ans[2] = y;
        s[1] = '-';
        return true;
    }
    else if(x * y == 24) {
        ans[1] = x, ans[2] = y;
        s[1] = '*';
        return true;
    }
    else if(y) {
        if(x % y == 0) {
            if(x / y == 24) {
                ans[1] = x, ans[2] = y;
                s[1] = '/';
                return true;
            }
        }
    }
    return false;
}
bool dfs2(int x, int y, int z) {
    if(x < y) swap(x, y);
    if(dfs3(x+y, z)) {
        ans[3] = x, ans[4] = y, ans[11] = x+y;
        s[2] = '+';
        return true;
    }
    if(dfs3(x-y, z)) {
        ans[3] = x, ans[4] = y, ans[11] = x-y;
        s[2] = '-';
        return true;
    }
    if(dfs3(x*y, z)) {
        ans[3] = x, ans[4] = y, ans[11] = x*y;
        s[2] = '*';
        return true;
    }
    if(y) {
        if(x % y == 0) {
            if(dfs3(x/y, z)) {
                ans[3] = x, ans[4] = y, ans[11] = x/y;
                s[2] = '/';
                return true;
            }
        }
    }
    return false;
}
bool dfs1(int x, int y, int n, int m) {
    if(x < y) swap(x, y);
    if(dfs2(x+y, n, m)) {
        ans[5] = x, ans[6] = y, ans[10] = x+y;
        s[3] = '+';
        return true;
    }
    if(dfs2(x-y, n, m)) {
        ans[5] = x, ans[6] = y, ans[10] = x-y;
        s[3] = '-';
        return true;
    }
    if(dfs2(x*y, n, m)) {
        ans[5] = x, ans[6] = y, ans[10] = x*y;
        s[3] = '*';
        return true;
    }
    if(y) {
        if(x % y == 0) {
            if(dfs2(x/y, n, m)) {
                ans[5] = x, ans[6] = y, ans[10] = x/y;
                s[3] = '/';
                return true;
            }
        }
    }
    return false;
}
void print() {
    cout<<ans[5]<<s[3]<<ans[6]<<"="<<ans[10]<<endl;
    cout<<ans[3]<<s[2]<<ans[4]<<"="<<ans[11]<<endl;
    cout<<ans[1]<<s[1]<<ans[2]<<"=24";
}
int main() {
    scanf("%d%d%d%d", &a, &b, &c, &d);
    if(dfs1(a, b, c, d)) {
        flag = 1;
        print();
        return 0;
    }
    if(dfs1(a, c, b, d)) {
        flag = 1;
        print();
        return 0;
    }
    if(dfs1(a, d, b, c)) {
        flag = 1;
        print();
        return 0;
    }
    if(dfs1(b, c, a, d)) {
        flag = 1;
        print();
        return 0;
    }
    if(dfs1(b, d, a, c)) {
        flag = 1;
        print();
        return 0;
    }
    if(dfs1(c, d, a, b)) {
        flag = 1;
        print();
        return 0;
    }
    if(!flag) printf("No answer!");
    return 0;
}

但数据‘1 3 5 7’过不了qwq

但luogu数据水我能过qwq