POJ 3368 Frequent values 线段树

文字解释见http://hi.baidu.com/lewutian/blog/item/d0e058ea85b780d8d539c9bf.html

/*
ID: sdj22251
PROG: subset
LANG: C++
*/
#include <iostream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cmath>
#include <ctime>
#define MAXN 111111
#define MAXM 104444
#define INF 100000000
#define PI acos(-1.0)
#define eps 1e-12
#define L(X) X<<1
#define R(X) X<<1|1
using namespace std;
struct PP
{
    int left, right, num;
}p[MAXN];
struct node
{
    int left, right, mid;
    int mx;
}tree[4 * MAXN];
int v[MAXN], h[MAXN];
int n, m, len;
void get()
{
    len = 1;
    p[1].left = 1;
    p[1].num = 1;
    h[1] = 1;
    for(int i = 2; i <= n; i++)
    {
        if(v[i] == v[i - 1])
        p[len].num++;
        else
        {
            p[len++].right = i - 1;
            p[len].left = i;
            p[len].num = 1;
        }
        h[i] = len;
    }
    p[len].right = n;
}
void up(int C)
{
    tree[C].mx = max(tree[L(C)].mx, tree[R(C)].mx);
}
void make_tree(int s, int e, int C)
{
    tree[C].left = s;
    tree[C].right = e;
    tree[C].mid = (s + e) >> 1;
    if(s == e){tree[C].mx = p[s].num; return;}
    make_tree(s, tree[C].mid, L(C));
    make_tree(tree[C].mid + 1, e, R(C));
    up(C);
}
int query(int s, int e, int C)
{
    if(tree[C].left >= s && tree[C].right <= e) return tree[C].mx;
    int ret = 0;
    if(tree[C].mid >= s) {int t = query(s, e, L(C)); ret = max(ret, t);}
    if(tree[C].mid < e) {int t = query(s, e, R(C)); ret = max(ret, t);}
    return ret;
}
int in()
{
    int flag = 1;
    char ch;
    int a = 0;
    while((ch = getchar()) == ' ' || ch == '\n');
    if(ch == '-') flag = -1;
    else
    a += ch - '0';
    while((ch = getchar()) != ' ' && ch != '\n')
    {
        a *= 10;
        a += ch - '0';
    }
    return flag * a;
}
void out(int a)
{
    if(a < 0) {putchar('-'); a = -a;}
    if(a >= 10)out(a / 10);
    putchar(a % 10 + '0');
}
int main()
{
    while(scanf("%d", &n) != EOF && n)
    {
        scanf("%d", &m);
        for(int i = 1; i <= n; i++) v[i] = in();
        get();
        make_tree(1, len, 1);
        for(int i = 1; i <= m; i++)
        {
            int x, y;
            x= in();
            y = in();
            int u = h[x];
            int v = h[y];
            if(u == v) out(y - x + 1);
            else if(u == v - 1) out(max(p[u].right - x + 1, y - p[v].left + 1));
            else
            {
                int ans = max(p[u].right - x + 1, y - p[v].left + 1);
                int t = query(u + 1, v - 1, 1);
                ans = max(ans, t);
                out(ans);
            }
            putchar('\n');
        }
    }
    return 0;
}