51Nod-1254-最大子段和 V2

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ACM模版
描述

题解

懒得写了，去讨论区看看佐理慧学姐的题解吧。炒鸡强的佐学姐~~~
代码

#include <cstdio>#include <iostream>using namespace std;typedef long long ll;const int MAXN = 5e4 + 10;int n;ll A[MAXN];ll mx_l[MAXN];ll mx_r[MAXN];ll dp_l[2][MAXN];ll dp_r[2][MAXN];template <class T>inline bool scan_d(T &ret){    char c;    int sgn;    if (c = getchar(), c == EOF)    {        return 0; //EOF    }    while (c != '-' && (c < '0' || c > '9'))    {        c = getchar();    }    sgn = (c == '-') ? -1 : 1;    ret = (c == '-') ? 0 : (c - '0');    while (c = getchar(), c >= '0' && c <= '9')    {        ret = ret * 10 + (c - '0');    }    ret *= sgn;    return 1;}int main(){    scan_d(n);    ll g = 0;    for (int i = 0; i < n; i++)    {        scan_d(A[i]);        g += A[i];    }    mx_l[0] = A[0];    for (int i = 1; i < n; i++)    {        mx_l[i] = max(mx_l[i - 1], A[i]);    }    mx_r[n - 1] = A[n - 1];    for (int i = n - 2; i >= 0; i--)    {        mx_r[i] = max(mx_r[i + 1], A[i]);    }    for (ll i = 1, sum = A[0], t = 0; i < n; i++)    {        if (sum < 0)        {            sum = 0;            t = i;        }        dp_l[0][i] = t;        dp_l[1][i] = sum;        sum += A[i];    }    ll sum = A[n - 1];    dp_r[0][n - 1] = n - 1;    dp_r[1][n - 1] = 0;    for (int i = n - 2, t = n - 1; i >= 0; i--)    {        if (sum < 0)        {            sum = 0;            t = i;        }        dp_r[0][i] = t;        dp_r[1][i] = sum;        sum += A[i];    }    ll tmp, tep, cnt;    g = max(0ll, g);    for (int i = 0; i < n; i++)    {        if (A[i] < 0)        {            if (dp_l[0][i] > 0 && dp_r[0][i] < n - 1)            {                tmp = dp_l[1][i] + dp_r[1][i] + max(mx_l[dp_l[0][i] - 1], mx_r[dp_r[0][i] + 1]);                tmp = max(tmp, dp_l[1][i] + dp_r[1][i]);            }            else if (dp_l[0][i] > 0)            {                tmp = dp_l[1][i] + dp_r[1][i] + mx_l[dp_l[0][i] - 1];                tmp = max(tmp, dp_l[1][i] + dp_r[1][i]);            }            else if (dp_r[0][i] < n - 1)            {                tmp = dp_l[1][i] + dp_r[1][i] + mx_r[dp_r[0][i] + 1];                tmp = max(tmp, dp_l[1][i] + dp_r[1][i]);            }            else            {                tmp = dp_l[1][i] + dp_r[1][i];            }            tep = dp_l[1][i] + dp_r[1][i];            cnt = 1;            while (A[dp_l[0][i] + cnt] < 0 && dp_l[0][i] + cnt < i)            {                tep += -A[dp_l[0][i] + cnt];                cnt++;            }            tmp = max(tmp, tep);            tep = dp_l[1][i] + dp_r[1][i];            cnt = 1;            while (A[dp_r[0][i] - cnt] < 0 && dp_r[0][i] - cnt > i)            {                tep += -A[dp_r[0][i] - cnt];                cnt++;            }            tmp = max(tmp, tep);            g = max(tmp, g);        }    }    printf("%lld\n", g);    return 0;}
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