#include <iostream>

#include <stack>

using namespace std;


int min(int n,int m)
{
    if (n>m)
    {
        return m;
    }
    else
        return n;
}

int water(int a[],int n)
{
    int i;
    const int count=n;
    int b[count];
    int c[count];
    int sum1=0;
    for (i = 1; i < count; i++)
    {
        if (a[i]>sum1)
        {
            sum1=a[i];
        }
        b[i]=sum1;
    }

    int j;
    int sum2=0;
    for (j = count-2; j >=0; j--)
    {
        if (a[j]>sum2)
        {
            sum2=a[j];
        }
        c[j]=sum2;
    }

    int sum=0;
    int k;
    for (k = 1; k < count-1; k++)
    {
        sum+=min(b[k],c[k])-a[k];
    }
    return sum;
}


int water2(int a[],int n)
{
    int i=0;
    int max=0;
    int pos=0;
    for (i = 0; i < n; i++)
    {
        if(a[i]>max)
        {
            max=a[i];
            pos=i;
        }
    }
    int j;
    int sum1=a[0];
    int ans=0;
    for (j = 1; j < pos; j++)
    {
        if (a[j]>=sum1)
        {
            sum1=a[j];
        }
        else
        {
            ans+=sum1-a[j];
        }
    }
    int sum2=a[n-1];
    int k;
    for (k = n-2; k>pos; k--)
    {
        if (a[k]>sum2)
        {
            sum2=a[k];
        }
        else
        {
            ans+=sum2-a[k];
        }
    }
    return ans;
}

int water3(int a[], int n)
{
    stack<pair<int, int>> s;
    int water = 0;
    for (int i = 0; i < n; ++i)
    {
        int height = 0;
        while (!s.empty())
        { // 将栈里比当前元素矮或等高的元素全部处理掉
        int bar = s.top().first;
        int pos = s.top().second;
        // bar, height, a[i] 三者夹成的凹陷
        water += (min(bar, a[i]) - height) * (i - pos - 1);
        height = bar;
        if (a[i] < bar) // 碰到了比当前元素高的，跳出循环
            break;
        else
            s.pop(); // 弹出栈顶，因为该元素处理完了，不再需要了
        }
        s.push(make_pair(a[i], i));
    }
    return water;
}



int main()
{
    int a[12]={0,1,0,2,1,0,1,3,2,1,2,1};
    int ans1=water(a,12);
    cout<<"ans1 is "<<ans1<<endl;

    int ans2=water2(a,12);
    cout<<"ans2 is "<<ans2<<endl;

    int ans3=water3(a,12);
    cout<<"ans3 is "<<ans3<<endl;
    return 0;
}