UV 1400 1400-"Ray, pass me the dishes! "(Line segment tree)

UV 1400-"Ray, pass me the dishes! "

Question Link

Question: Given a sequence, ask for a [L, R] interval each time, and find the maximum continuous subsequence and

Idea: Line Segment tree, each node maintains three values, the maximum continuous subsequence, the maximum continuous prefix sequence, and the maximum continuous suffix sequence. When pushup is performed, create a new node based on the three sequences.

Code:

#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;}