【HDOJ】1506 Largest Rectangle in a Histogram

Twitter还是Amazon拿这个题目当过面试题。DP区间求面积。

 /* 1506 */
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>

 #define MAXN 100005
 #define INF 999999

 int l[MAXN], r[MAXN];
 __int64 a[MAXN];

 __int64 max(__int64 a, __int64 b) {
     return a>b ? a:b;
 }

 int main() {
     int n;
     int i, j, k;
     __int64 ans;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
     #endif

     while (scanf("%d",&n)!=EOF && n) {
         for (i=; i<=n; ++i)
             scanf("%I64d", &a[i]);
         a[] = a[n+] = -INF;
         l[] = ;
         for (i=; i<=n; ++i) {
             if (a[i-] < a[i]) {
                 l[i] = i;
             } else {
                 j = i;
                 while (j--) {
                     if (a[j] < a[i]) {
                         l[i] = j+;
                         break;
                     } else {
                         j = l[j];
                     }
                 }
             }
         }
         r[n+] = n+;
         for (i=n; i>; --i) {
             if (a[i+] < a[i]) {
                 r[i] = i;
             } else {
                 j = i;
                 while (j++ <= n) {
                     if (a[j] < a[i]) {
                         r[i] = j - ;
                         break;
                     } else {
                         j = r[j];
                     }
                 }
             }
         }

         ans = -INF;
         for (i=; i<=n; ++i) {
             ans = max(ans, a[i]*(r[i]-l[i]+));
         }
         printf("%I64d\n", ans);
     }

     return ;
 }