[hdu1506]单调队列（栈）

题意：http://acm.hdu.edu.cn/showproblem.php?pid=1506看图一目了然。两个方向单调队列维护下。

 1 #include <iostream>

 2 #include <cstdio>

 3 #include <algorithm>

 4 #include <cstdlib>

 5 #include <cstring>

 6 #include <map>

 7 #include <queue>

 8 #include <deque>

 9 #include <cmath>

10 #include <vector>

11 #include <ctime>

12 #include <cctype>

13 #include <set>

14 

15 using namespace std;

16 

17 #define mem0(a) memset(a, 0, sizeof(a))

18 #define lson l, m, rt << 1

19 #define rson m + 1, r, rt << 1 | 1

20 #define define_m int m = (l + r) >> 1

21 #define Rep(a, b) for(int a = 0; a < b; a++)

22 #define lowbit(x) ((x) & (-(x)))

23 #define constructInt4(name, a, b, c, d) name(int a = 0, int b = 0, int c = 0, int d = 0): a(a), b(b), c(c), d(d) {}

24 #define constructInt3(name, a, b, c) name(int a = 0, int b = 0, int c = 0): a(a), b(b), c(c) {}

25 #define constructInt2(name, a, b) name(int a = 0, int b = 0): a(a), b(b) {}

26 

27 typedef double db;

28 typedef long long LL;

29 typedef pair<int, int> pii;

30 typedef multiset<int> msi;

31 typedef multiset<int>::iterator msii;

32 typedef set<int> si;

33 typedef set<int>::iterator sii;

34 

35 const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};

36 const int dy[8] = {0, -1, 0, 1, -1, 1, 1, -1};

37 const int maxn = 1e6 + 7;

38 const int maxm = 1e5 + 7;

39 const int MD = 1e9 +7;

40 const int INF = 1e9 + 7;

41 

42 template<class T> struct MonotoneQueue{

43     deque<T> Q;

44     MonotoneQueue<T>() { Q.clear(); }

45     void clear() { Q.clear(); }

46     bool empty() { return Q.empty(); }

47     void add_back(T x) { while (!Q.empty() && !(Q.back() < x)) Q.pop_back(); Q.push_back(x); }

48     void pop_front() { Q.pop_front(); }

49     T back2() { return *(Q.end() - 2); }

50     T front() { return Q.front(); }

51 };

52 

53 struct pair1 {

54     int val, pos;

55     bool operator < (const pair1 &a) const {

56         return val < a.val;

57     }

58     constructInt2(pair1, val, pos);

59 };

60 

61 MonotoneQueue<pair1> UQ;

62 

63 int a[100010], L[100010];

64 

65 int main() {

66     //freopen("in.txt", "r", stdin);

67     int n;

68     while (cin >> n, n) {

69         UQ.clear();

70         UQ.add_back(pair1(-1, -1));

71         for (int i = 0; i < n; i++) {

72             scanf("%d", a + i);

73             UQ.add_back(pair1(a[i], i));

74             L[i] = UQ.back2().pos + 1;

75         }

76         UQ.clear();

77         UQ.add_back(pair1(-1, n));

78         LL ans = 0;

79         for (int i = n - 1; i >= 0; i--) {

80             UQ.add_back(pair1(a[i], i));

81             ans = max(ans, (LL)a[i] * (UQ.back2().pos - L[i]));

82         }

83         cout << ans << endl;

84     }

85     return 0;

86 }

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