UVA 1400 1400 - Ray, Pass me the dishes!(线段树)

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UVA 1400 - "Ray, Pass me the dishes!"

题目链接

题意：给定一个序列，每次询问一个[L,R]区间，求出这个区间的最大连续子序列和

思路：线段树，每个节点维护3个值，最大连续子序列，最大连续前缀序列，最大连续后缀序列，那么每次pushup的时候，根据这3个序列去拼凑得到新的一个结点即可

代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;#define lson(x) ((x<<1) + 1)
#define rson(x) ((x<<1) + 2)
#define MP(a, b) make_pair(a, b)typedef long long ll;
typedef pair<int, int> Point;const int N = 500005;int n, m;
ll a[N], sum[N];struct Node {int l, r;int prex, sufx;Point sub;
} node[4 * N];ll get(Point x) {return sum[x.second] - sum[x.first - 1];
}bool Max(Point a, Point b) {long long sa = get(a);long long sb = get(b);if (sa != sb) return sa > sb;return a < b;
}Point Maxsub(Node a, Node b) {Point ans;if (Max(a.sub, b.sub)) ans = a.sub;else ans = b.sub;if (Max(MP(a.sufx, b.prex), ans)) ans = MP(a.sufx, b.prex);return ans;
}int Maxpre(Node a, Node b) {Point ans = MP(a.l, a.prex);if (Max(MP(a.l, b.prex), ans)) ans = MP(a.l, b.prex);return ans.second;
}int Maxsuf(Node a, Node b) {Point ans = MP(b.sufx, b.r);if (Max(MP(a.sufx, b.r), ans)) ans = MP(a.sufx, b.r);return ans.first;
}Node pushup(Node a, Node b) {Node ans;ans.l = a.l; ans.r = b.r;ans.sub = Maxsub(a, b);ans.prex = Maxpre(a, b);ans.sufx = Maxsuf(a, b);return ans;
}void build(int l, int r, int x) {if (l == r) {node[x].l = l; node[x].r = r;node[x].prex = node[x].sufx = l;node[x].sub = MP(l, l);return ;}int mid = (l + r) / 2;build(l, mid, lson(x));build(mid + 1, r, rson(x));node[x] = pushup(node[lson(x)], node[rson(x)]);
}Node Query(int l, int r, int x) {if (l <= node[x].l && r >= node[x].r)return node[x];int mid = (node[x].l + node[x].r) / 2;Node ans;if (l <= mid && r > mid)ans = pushup(Query(l, r, lson(x)), Query(l, r, rson(x)));else if (l <= mid) ans = Query(l, r, lson(x));else if (r > mid) ans = Query(l, r, rson(x));return ans;
}int main() {int cas = 0;while (~scanf("%d%d", &n, &m)) {for (int i = 1; i <= n; i++) {scanf("%lld", &a[i]);sum[i] = sum[i - 1] + a[i];}build(1, n, 0);printf("Case %d:\n", ++cas);int a, b;while (m--) {scanf("%d%d", &a, &b);Node ans = Query(a, b, 0);printf("%d %d\n", ans.sub.first, ans.sub.second);}}return 0;
}

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