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;}