51nod 1174 区间中最大的数【线段树】

题目链接：http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1174

#include <stdio.h>
#include <iostream>
#include <string>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <vector>

#define Mid(a,b) ( a+((b-a)>>1))
#define ll(x) (x<<1)
#define rr(x) (x<<1|1)

const int N = 100100;

using namespace std;

int t, n;

int a
;

struct node
{
int left;
int right;
int sum;
int mid() { return Mid(left, right); }
};

struct segtree
{
node tree[N * 4];

void buildtree(int left, int right, int ind)
{
tree[ind].left = left;
tree[ind].right = right;
tree[ind].sum = 0;

if (left == right)
tree[ind].sum = a[left];
else
{
int mid = tree[ind].mid();
buildtree(left, mid, ll(ind));
buildtree(mid + 1, right, rr(ind));
tree[ind].sum = max(tree[ll(ind)].sum, tree[rr(ind)].sum);
}
}

int query(int st, int ed, int ind)
{
int left = tree[ind].left;
int right = tree[ind].right;

if (st <= left && right <= ed)
return tree[ind].sum;
else
{
int mid = tree[ind].mid();
int sum1 = 0;
int sum2 = 0;
if (st <= mid)
sum1 = query(st, ed, ll(ind));
if (ed > mid)
sum2 = query(st, ed, rr(ind));

return max(sum1, sum2);
}
}
}seg;

int main()
{
while (scanf("%d", &n) != EOF)
{
for (int i = 1; i <= n; i++)
{
scanf("%d", &a[i]);
}

seg.buildtree(1, n, 1);

int m;
scanf("%d", &m);
while(m--)
{
int c, d;
scanf("%d%d", &c, &d);
printf("%d\n", seg.query(c + 1, d + 1, 1));
}
}
return 0;
}