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 = ;

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

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

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