C++ 关于数组最大内存

大家看一下两种代码：

#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

typedef struct point
{
	int x;
	int y;
}Node;

bool cmp(point a, point b)
{
	return a.y == b.y ? a.x > b.x:a.y < b.y;
}

int main()
{
	int pointNum = 0;
	cout << "输入点的个数：";
	cin >> pointNum;

	Node list[500001];

	for (int i = 0; i < pointNum; i++)
	{
		scanf("%d %d", &list[i].x, &list[i].y);
	}

	sort(list, list+pointNum, cmp);
	int maxx = -1;
	for (int i = pointNum; i >=0; i--)
	{
		if (list[i].x >= maxx)
		{
			printf("%d %d\n", list[i].x, list[i].y);
			maxx = list[i].x;
		}
	}
	return 0;
}

#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

typedef struct