Greedy (1)

1. Interval problem

1.1 Interval selection point 

#include<iostream>
#include<algorithm>

using namespace std;

const int N = 100010;

int n;
struct Range
{
    int l,r;
    bool operator < (const Range &w)const
    {
        return r < w.r;
    }
}range[N];

int main()
{
    scanf("%d",&n);
    for(int i = 0;i < n;i ++)
    {
        int l,r;
        scanf("%d%d",&l,&r);
        range[i] = {l,r};
    }
    sort(range,range + n);
    int res = 0,ed = -2e9;
    for(int i = 0;i < n;i ++)
        if(range[i].l > ed)
        {
            res ++;
            ed = range[i].r;
        }

    printf("%d\n",res);

    return 0;
}

1.2 Maximum number of disjoint intervals

#include<iostream>
#include<algorithm>

using namespace std;

const int N = 100010;

int n;
struct Range
{
    int l,r;
    bool operator < (const Range &w)const
    {
        return r < w.r;
    }
}range[N];

int main()
{
    scanf("%d",&n);
    for(int i = 0;i < n;i ++)
    {
        int l,r;
        scanf("%d%d",&l,&r);
        range[i] = {l,r};
    }
    sort(range,range + n);
    int res = 0,ed = -2e9;
    for(int i = 0;i < n;i ++)
        if(range[i].l < ed)
        {
            res ++;
            ed = range[i].r;
        }

    printf("%d\n",res);

    return 0;
}

 1.3 Interval grouping

 

 

2. Huffman tree

Merge fruit

Pick the smallest two piles from all the piles and merge them each time

#include<iostream>
#include<algorithm>
#include<queue>

using namespace std;

int main()
{
    int n;
    scanf("%d",&n);

    priority_queue<int,vector<int>,greater<int>>heap;
    while(n --)
    {
        int x;
        scanf("%d",&x);
        heap.push(x);
    }
    int res = 0;

    while(heap.size() > 1)
    {
        int a = heap.top(); heap.pop();
        int b = heap.top(); heap.pop();
        res += a + b;
        heap.push(a + b);
    }

    printf("%d\n",res);
    return 0;
}