hdu 5583 Kingdom of Black and White（高效）

题目链接：hdu 5583 Kingdom of Black and White

代码

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
const int maxn = 1e5 + 5;
typedef long long ll;

char str[maxn];
int L[maxn][2], R[maxn][2];

ll solve () {
    int n = strlen(str+1);
    memset(L, 0, sizeof(L));
    memset(R, 0, sizeof(R));

    for (int i = 1; i <= n; i++) {
        int d = str[i] - '0';
        L[i][d] = L[i-1][d] + 1;
    }
    for (int i = n; i; i--) {
        int d = str[i] - '0';
        R[i][d] = R[i+1][d] + 1;
    }

    ll sum = 0;
    for (int i = 1; i <= n; i++) if (str[i] != str[i+1]) {
        int d = str[i] - '0';
        sum += 1LL * L[i][d] * L[i][d];
    }

    ll ans = sum;
    for (int i = 1; i <= n; i++) {
        int t = str[i] - '0';
        ll al = i > 1 ? L[i-1][str[i-1]-'0'] : 0, am = 1, ar = i < n ? R[i+1][str[i+1]-'0'] : 0;
        ll dl = al, dm = am, dr = ar;
        if (dl && str[i-1] == str[i]) { dm += dl; dl = 0; }
        else if (al) { am += al; al = 0; }

        if (dr && str[i+1] - '0' == t) { dr += dm; dm = 0; }
        else if (ar) { ar += am; am = 0; }

        ll add = al * al + am * am + ar * ar;
        ll del = dl * dl + dm * dm + dr * dr;
        //printf("+%lld %lld %lld -%lld %lld %lld\n", al, am, ar, dl, dm, dr);
        ans = max(ans, sum + add - del);
    }
    return ans;
}

int main () {
    int cas;
    scanf("%d", &cas);
    for (int kcas = 1; kcas <= cas; kcas++) {
        scanf("%s", str+1);
        printf("Case #%d: %lld\n", kcas, solve());
    }
    return 0;
}