Trainning Guide的代码

今天无意间找到了训练指南的网上代码，都是刘汝佳写的，在这。

今天在做这题1400 - "Ray, Pass me the dishes!"，我写的线段树的思路跟上次的Frequent Sequence的思路类似，维护区间上从左端点开始、从右端点开始，中间部分的最优序列，查了半天，没查到问题，先把代码备份上来。

#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;

const int MAXN = 500005;

typedef long long int64;

int dish[MAXN];
int64 dish_sum[MAXN];

int64 get_sum(int L, int R) {
    return dish_sum[R] - dish_sum[L - 1];
}

class SegNode {
public:
    int L, R;
    int L_end, R_beg;
    int beg, end;
    int64 LR_sum() { return get_sum(L, R); }
    int64 L_sum() { return get_sum(L, L_end); }
    int64 R_sum() { return get_sum(R_beg, R); }
    int64 sum() { return get_sum(beg, end); }
    void log() {
        printf("[%d %d]: (%d %d), (%d %d), (%d %d).
",
            L, R, L, L_end, R_beg, R, beg, end); 
    }
} node[5 * MAXN];

class SegTree {
public:
    void build(int r, int L, int R) {
        node[r].L = L;
        node[r].R = R;
        if (L == R) {
            // leaf
            node[r].L_end = R;
            node[r].R_beg = L;
            node[r].beg = L;
            node[r].end = R;
        } else {
            // non leaf
            int M = (L + R) / 2;
            build(2 * r, L, M);
            build(2 * r + 1, M + 1, R);

            // left 
            node[r].L_end = node[2 * r].L_end;
            if (node[2 * r].LR_sum() + node[2 * r + 1].L_sum() > node[2 * r].L_sum()) {
                node[r].L_end = node[2 * r + 1].L_end;
            }

            // right
            node[r].R_beg = node[2 * r + 1].R_beg;
            if (node[2 * r + 1].LR_sum() + node[2 * r].R_sum() > node[2 * r + 1].R_sum()) {
                node[r].R_beg = node[2 * r].R_beg; 
            }
            
            // mid
            if (node[2 * r].sum() >= node[2 * r + 1].sum()) {
                node[r].beg = node[2 * r].beg;
                node[r].end = node[2 * r].end;
            } else {
                node[r].beg = node[2 * r + 1].beg;
                node[r].end = node[2 * r + 1].end;
            }
            if (node[2 * r].R_sum() + node[2 * r + 1].L_sum() > node[r].sum()) {
                node[r].beg = node[2 * r].R_beg;
                node[r].end = node[2 * r + 1].L_end;
            }
        }
        //node[r].log();
    }
    void query(int r, int L, int R, int& left, int& right, int k) {
        if (L <= node[r].L && node[r].R <= R) {
            if (k == 0) { left = node[r].L; right = node[r].L_end; } 
            else if (k == 1) { left = node[r].R_beg; right = node[r].R; }
            else { left = node[r].beg; right = node[r].end; }
        } else {
            if (R <= node[2 * r].R) {
                query(2 * r, L, R, left, right, k);
            } else if (L >= node[2 * r + 1].L) {
                query(2 * r + 1, L, R, left, right, k);
            } else {
                int left_beg, left_end, right_beg, right_end;
                query(2 * r, L, R, left_beg, left_end, k);
                query(2 * r + 1, L, R, right_beg, right_end, k);
                if (k == 0) {
                    left = left_beg;
                    right = left_end;
                    if (get_sum(left_beg, right_end) > get_sum(left, right)) {
                        left = left_beg;
                        right = right_end;
                    }                    
                } else if (k == 1) {
                    left = right_beg;
                    right = right_end;
                    if (get_sum(left_beg, right_end) > get_sum(left, right)) {
                        left = left_beg;
                        right = right_end;
                    }
                } else {
                    if (get_sum(left_beg, left_end) >= get_sum(right_beg, right_end)) {
                        left = left_beg;
                        right = left_end;
                    } else {
                        left = right_beg;
                        right = right_end;
                    }
                    int m_l, m_r, x;
                    query(2 * r, L, R, m_l, x, 1);
                    query(2 * r + 1, L, R, x, m_r, 0);
                    if (get_sum(m_l, m_r) > get_sum(left, right)) {
                        left = m_l;
                        right = m_r;
                    } 
                } 
            }
        } 
    }
} tree;

int main() {
    int n, m, c = 0;
    while (scanf("%d%d", &n, &m) != EOF) {
        dish_sum[0] = 0;
        for (int i = 1; i <= n; i++) {
            scanf("%d", &dish[i]);
            dish_sum[i] = dish_sum[i - 1] + dish[i];
        }
        tree.build(1, 1, n);
        printf("Case %d:
", ++c);
        for (int i = 0; i < m; i++) {
            int l, r, left, right;
            scanf("%d%d", &l, &r);
            if (l > r) swap(l, r);
            l = max(1, l);
            r = min(n, r);
            tree.query(1, l, r, left, right, 2);
            printf("%d %d
", left, right);
        }
    }
}