【SPOJ】1043 Can you answer these queries I

操作：查询区间最大连续和。

每个节点保存当前区间往左，往右的最大和。

往左最大连续和=max（左区间往左最大连续和，左区间的和+右区间往左最大连续和）。

区间最大值=max（左，右区间最大值，左区间右连续+右区间左连续）。

返回答案时，区间需要不断的合并。

 1 #include<cstdio>

 2 #define MAX(a,b) ((a)>(b)?(a):(b))

 3 #define MAXN 50010

 4 #define oo 1000000000

 5 struct node {

 6     int left, right, sum, val;

 7     void Init() {

 8         sum = 0;

 9         left = right = val = -oo;

10     }

11 };

12 node tree[MAXN << 2];

13 inline void PushUp(int rt) {

14     tree[rt].left = MAX(tree[rt << 1].left,

15             tree[rt << 1].sum + tree[rt << 1 | 1].left);

16     tree[rt].right = MAX(tree[rt << 1 | 1].right,

17             tree[rt << 1 | 1].sum + tree[rt << 1].right);

18     tree[rt].sum = tree[rt << 1].sum + tree[rt << 1 | 1].sum;

19     tree[rt].val = MAX(tree[rt << 1].val, tree[rt << 1 | 1].val);

20     tree[rt].val = MAX(tree[rt].val,

21             tree[rt << 1].right + tree[rt << 1 | 1].left);

22 }

23 void Build(int L, int R, int rt) {

24     if (L == R) {

25         scanf("%d", &tree[rt].val);

26         tree[rt].left = tree[rt].right = tree[rt].sum = tree[rt].val;

27     } else {

28         int mid = (L + R) >> 1;

29         Build(L, mid, rt << 1);

30         Build(mid + 1, R, rt << 1 | 1);

31         PushUp(rt);

32     }

33 }

34 node Query(int x, int y, int L, int R, int rt) {

35     if (x <= L && R <= y)

36         return tree[rt];

37     int mid = (L + R) >> 1;

38     node a, b, res;

39     a.Init(), b.Init(), res.Init();

40     if (x <= mid)

41         a = Query(x, y, L, mid, rt << 1);

42     if (y > mid)

43         b = Query(x, y, mid + 1, R, rt << 1 | 1);

44     res.left = MAX(a.left, a.sum + b.left);

45     res.right = MAX(b.right, b.sum + a.right);

46     res.sum = a.sum + b.sum;

47     res.val = MAX(a.val, b.val);

48     res.val = MAX(res.val, a.right + b.left);

49     return res;

50 }

51 int main() {

52     int n, q, x, y;

53     while (~scanf("%d", &n)) {

54         Build(1, n, 1);

55         scanf("%d", &q);

56         while (q--) {

57             scanf("%d%d", &x, &y);

58             printf("%d\n", Query(x, y, 1, n, 1).val);

59         }

60     }

61     return 0;

62 }