[NOI 2014] 起床困难综合征

[题目链接]

         https://www.lydsy.com/JudgeOnline/problem.php?id=3668

[算法]

        从高位向低位贪心即可

        时间复杂度 ： O(30N)

[代码]

       

#include<bits/stdc++.h>
using namespace std;
#define MAXLOG 30
const int MAXN = 1e5 + 10;

int n,m,ans;
int value[MAXN],t[MAXN];
char op[5];

template <typename T> inline void read(T &x)
{
    int f = 1; x = 0;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
    for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
    x *= f;
}
inline bool ok(int x,int val)
{
        int num;
        num = (val == 0) ? 0 : 1 << x; 
        for (int i = 1; i <= n; i++)        
        {
                if (value[i] == 1) num &= t[i];
                if (value[i] == 2) num |= t[i];
                if (value[i] == 3) num ^= t[i];
        }
        if (num & (1 << x)) return true;
        else return false;
}

int main() 
{

        
        scanf("%d%d",&n,&m);
        for (int i = 1; i <= n; i++)
        {
                scanf("%s%d",op,&t[i]);
                if (strcmp(op,"AND") == 0) value[i] = 1;
                if (strcmp(op,"OR") == 0) value[i] = 2;
                if (strcmp(op,"XOR") == 0) value[i] = 3;
        }
        for (int i = MAXLOG; i >= 0; i--)
        {
                if (ok(i,0)) 
                {
                        ans += 1 << i;
                        continue;
                }
                if (ok(i,1) && m >= 1 << i) 
                {
                        m -= 1 << i;
                        ans += 1 << i;
                }
        }
        printf("%d
",ans);
        
        return 0;
    
}