51Nod 1272最大距离 （树状数组维护前缀最小值）

题目链接 最大距离

其实主流解法应该是单调栈……我用了树状数组。

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)    for (int i(a); i <= (b); ++i)

const int N = 100010;

struct node{
    int x, y;
    friend bool operator < (const node &a, const node &b){
        return a.x == b.x ? a.y < b.y : a.x < b.x; 
    }
        //sort细节，初始ID在前的最后也要在前
} a[N];

int f[N];
int n, ans;

void update(int x, int val){
    for (; x <= n; x += x & -x) f[x] = min(f[x], val);
}

//树状数组更新

int query(int x){
    int ret = 1 << 30;
    for (; x; x -= x & -x) ret = min(ret, f[x]);
    return ret;
}

//树状数组查询前缀最小值

int main(){

    scanf("%d", &n);
    rep(i, 1, n){
        scanf("%d", &a[i].x);
        a[i].y = i;
    }

    sort(a + 1, a + n + 1);
    rep(i, 0, n + 100) f[i] = 1 << 30; //Init...

    ans = -1;
    rep(i, 1, n){
        update(a[i].y, a[i].y);
        int cnt = query(a[i].y);
        ans = max(ans, a[i].y - cnt);
    }
    printf("%d
", ans);
    return 0;
}