题目链接

以为是个线段树，结果写到一半写不出来了。。
赛后看别人代码发现是思维

AC代码：

/*
 * @Author: hesorchen
 * @Date: 2020-04-14 10:33:26
 * @LastEditTime: 2020-05-31 17:44:16
 * @Link: https://hesorchen.github.io/
 */
#include <map>
#include <set>
#include <list>
#include <queue>
#include <deque>
#include <cmath>
#include <stack>
#include <vector>
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define endl '\n'
#define PI cos(-1)
#define PB push_back
#define ll long long
#define INF 0x3f3f3f3f
#define mod 998244353
#define lowbit(abcd) (abcd & (-abcd))
#define max(a, b) ((a > b) ? (a) : (b))
#define min(a, b) ((a < b) ? (a) : (b))
#define IOS                      \
    ios::sync_with_stdio(false); \
    cin.tie(0);                  \
    cout.tie(0);
#define FRE                              \
    {                                    \
        freopen("in.txt", "r", stdin);   \
        freopen("out.txt", "w", stdout); \
    }

inline ll read()
{
    ll x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
    {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    return x * f;
}
//==============================================================================

ll a[100010];
int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        ll n;
        n = read();
        for (int i = 1; i <= n; i++)
            a[i] = read() - 1;
        ll maxx = 0;
        ll ans = 0;
        for (int i = 1; i <= n; i++)
        {
            if (a[i] > maxx)
                ans += a[i] - maxx, maxx = max(maxx, a[i]);
            else
                maxx = a[i];
        }
        cout << ans << endl;
    }
    return 0;
}
/*
0 2 4 1 6 0
*/