uva1400线段树

　　题意：在l,r区间找到 最靠近左边的和最大区间。

要理清思路写。简单区间合并。查找要麻烦点，三个查找函数，分别是向左范围内最大连续，向右范围内最大连续，整体最大连续。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <climits>
#include <string>
#include <iostream>
#include <map>
#include <cstdlib>
#include <list>
#include <set>
#include <queue>
#include <stack>
#include <math.h>
using namespace std;
typedef long long LL;

#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
const int maxn = 555555;
const LL INF = 1844674407370955161LL;
LL sum[maxn << 2], Max[maxn << 2], rmax[maxn << 2], lmax[maxn << 2];
int rl[maxn << 2], lr[maxn << 2], rpos[maxn << 2], lpos[maxn << 2], tfr[maxn << 2], tfl[maxn << 2];
int fl[maxn << 2], fr[maxn << 2];
void up(int l, int r, int rt)
{
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
    lmax[rt] = lmax[rt << 1]; rmax[rt] = rmax[rt << 1 | 1]; lr[rt] = lr[rt << 1]; rl[rt] = rl[rt << 1 | 1];
    LL k = rmax[rt << 1] + lmax[rt << 1 | 1];
    if (sum[rt << 1] + lmax[rt << 1 | 1] > lmax[rt]){
        lmax[rt] = sum[rt << 1] + lmax[rt << 1 | 1];
        lr[rt] = lr[rt << 1 | 1];
    }
    if (sum[rt << 1 | 1] + rmax[rt << 1] > rmax[rt << 1 | 1]){
        rmax[rt] = sum[rt << 1 | 1] + rmax[rt << 1];
        rl[rt] = rl[rt << 1];
    }
    if (lmax[rt] >= k&&lmax[rt] >= rmax[rt]){
        Max[rt] = lmax[rt]; lpos[rt] = l; rpos[rt] = lr[rt];
    }
    else
    if (k >= lmax[rt] && k >= rmax[rt]){
        Max[rt] = k, lpos[rt] = rl[rt << 1], rpos[rt] = lr[rt << 1 | 1];
    }
    else
        Max[rt] = rmax[rt], lpos[rt] = rl[rt], rpos[rt] = r;
}

void build(int l, int r, int rt)
{
    if (l == r){
        LL t;
        scanf("%lld",&t);
        sum[rt] = Max[rt] = lmax[rt] = rmax[rt] = t; lpos[rt]=rpos[rt]=lr[rt] = rl[rt] = l;
        return;
    }
    int mid = (l + r) >> 1;
    build(lson);
    build(rson);
    up(l, r, rt);
}

LL asks(int L, int R, int l, int r, int rt)
{
    if (L <= l&&r <= R) return sum[rt];
    int mid = (l + r) >> 1;
    LL ans = 0;
    if (L <= mid) ans += asks(L, R, lson);
    if (R > mid) ans += asks(L, R, rson);
    return ans;
}

LL askl(int L, int R, int l, int r, int rt)
{
    if (L <= l&&r <= R) {
        tfr[rt] = lr[rt];
        return lmax[rt];
    }
    int mid = (l + r) >> 1;
    LL ans1 = -INF; LL ans2 = -INF;
    if (L <= mid) ans1 = askl(L, R, lson);
    if (R > mid) ans2 = askl(L, R, rson);
    LL k = asks(L, R, lson);
    if (ans1 >= ans2 + k){
        tfr[rt] = tfr[rt << 1]; return ans1;
    }
    else {
        tfr[rt] = tfr[rt << 1 | 1]; return ans2 + k;
    }
}

LL askr(int L, int R, int l, int r, int rt)
{
    if (L <= l&&r <= R){
        tfl[rt] = rl[rt]; return rmax[rt];
    }
    int mid = (l + r) >> 1;
    LL ans1 = -INF; LL ans2 = -INF;
    if (L <= mid) ans1 = askr(L, R, lson);
    if (R > mid) ans2 = askr(L, R, rson);
    LL k = asks(L, R, rson);
    if (k + ans1 >= ans2){
        tfl[rt] = tfl[rt << 1]; return k + ans1;
    }
    else{
        tfl[rt] = tfl[rt << 1 | 1]; return ans2;
    }
}
LL ask(int L, int R, int l, int r, int rt)
{
    if (L <= l&&r <= R){
        fl[rt] = lpos[rt]; fr[rt] = rpos[rt];
        return Max[rt];
    }
    int mid = (l + r) >> 1;
    LL ans = -INF;
    if (L <= mid){
        LL k = ask(L, R, lson);
        if (k > ans){
            ans = k; fl[rt] = fl[rt << 1]; fr[rt] = fr[rt << 1];
        }
    }
    if (L <= mid&&R > mid){
        LL ans1 = askl(mid+1, R, rson); LL ans2 = askr(L, mid, lson);
        int tl = tfl[rt<<1]; int tr = tfr[rt<<1|1];
        if (ans1 + ans2 > ans) {
            ans = ans1 + ans2; fl[rt] = tl; fr[rt] = tr;
        }
    }
    if (R > mid){
        LL k = ask(L, R, rson);
        if (k > ans){
            ans = k; fl[rt] = fl[rt << 1 | 1]; fr[rt] = fr[rt << 1 | 1];
        }
    }
    return ans;
}
int main()
{
    int n, m, l, r;
    int Icase = 0;
    while (cin >> n >> m){
        build(1, n, 1);
        printf("Case %d:
", ++Icase);
        for (int i = 0; i < m; i++){
            scanf("%d%d", &l, &r);
            int  t = ask(l, r, 1, n, 1);
            printf("%d %d
", fl[1], fr[1]);
        }
    }
    return 0;
}