BZOJ2748(DP)

非常简单的DP题。类似背包的操作，按照音量改变值进行状态转移即可。

#include <bits/stdc++.h>

using namespace std;

#define REP(i,n)                for(int i(0); i <  (n); ++i)
#define rep(i,a,b)              for(int i(a); i <= (b); ++i)
#define dec(i,a,b)              for(int i(a); i >= (b); --i)
#define for_edge(i,x)           for(int i = H[x]; i; i = X[i])

#define LL      long long
#define ULL     unsigned long long
#define MP      make_pair
#define PB      push_back
#define FI      first
#define SE      second
#define INF     1 << 30

const int N     =    100000      +       10;
const int M     =    10000       +       10;
const int Q     =    1000        +       10;
const int A     =    30          +       1;

int a[N];
int f[A << 1][Q];
int n, init, up;
int x, ans;

int main(){
#ifndef ONLINE_JUDGE
    freopen("test.txt", "r", stdin);
    freopen("test.out", "w", stdout);
#endif

    memset(f, 0, sizeof f);
    scanf("%d%d%d", &n, &init, &up);
    rep(i, 1, n) scanf("%d", a + i);
    f[0][init] = 1;
    rep(i, 1, 50){
        rep(j, 0, up){
            x = j + a[i];
            if (x >= 0 && x <= up) f[i][j] |= f[i - 1][x];
            x = j - a[i];
            if (x >= 0 && x <= up) f[i][j] |= f[i - 1][x];
        }
    }

    ans = -1;
    dec(i, up, 0){
        if (f[n][i]){
            ans = i;
            break;
        }
    }
/*
    rep(i, 0, n){
        rep(j, 0, up) printf("%d", f[i][j]);
        putchar(10);
    }
*/
    printf("%d
", ans);

    return 0;

}