如何优化内存

#include<bits/stdc++.h>
using namespace std;
int n,m,k,v[20000][20000];
void mark(int i, int j, int x) {
	for (int k = 1; k <= n; k++) {
		v[k][j] = x;
	}
	for (int k=1;k<=m;k++){
		v[i][k] = x;
	}
	for (int k = n; k >= 1; k--) {
		v[k][j + k - i] = x;
	}
	for (int k = 1; k <= m; k++) {
		v[k][j + i - k] = x;
	}
}
int main(){
	cin>>n>>m>>k;
	int ans=0;
	for (int i=0;i<k;i++){
		int a,b;
		cin>>a>>b;
		mark(a,b,1);
	}
	for (int i=1;i<=n;i++){
		for (int j=1;j<=m;j++){
			if(v[i][j]!=1){
				ans++;
			}
		}
	}
	cout<<ans;
    return 0;
}

求答！