85 lines
1.9 KiB
C++
85 lines
1.9 KiB
C++
#include<cstdio>
|
|
#include<cstring>
|
|
#define L 1001000
|
|
|
|
int a,b,n,l,inf,dp[L];
|
|
int tree[4*L];
|
|
|
|
void updata(int *p, int rt, int l, int r,int pos, int k)
|
|
{
|
|
if (l==r) {
|
|
p[rt]=k;
|
|
return ;
|
|
}
|
|
int mid=(l+r)>>1;
|
|
if (pos<=mid) updata(p,rt<<1, l, mid, pos, k);
|
|
else updata(p, rt<<1|1, mid+1, r, pos, k);
|
|
int lv=p[rt<<1];
|
|
int rv=p[rt<<1|1];
|
|
p[rt]=lv<rv?lv:rv;
|
|
}
|
|
|
|
int query(int *p,int rt, int l,int r, int s, int e)
|
|
{
|
|
if(l==s && e==r) return p[rt];
|
|
int mid = (l+r)>>1;
|
|
if(e<=mid) return query(p, rt<<1, l, mid, s, e);
|
|
if(s>mid) return query(p, rt<<1|1, mid+1, r, s, e);
|
|
int lv=query(p,rt<<1, l, mid, s,mid);
|
|
int rv=query(p,rt<<1|1, mid+1, r, mid+1, e);
|
|
return lv<rv?lv:rv;
|
|
}
|
|
|
|
int dpro(void)
|
|
{
|
|
if(b<1) return -1;
|
|
dp[0]=0;
|
|
|
|
for(int j=0; j<4*L; j++) tree[j]=L*2;
|
|
|
|
for(int j=a; j<=b; j++){
|
|
if(dp[2*j]<=inf) dp[0+2*j] = dp[0]+1;
|
|
updata(tree,1, 1, l ,j,dp[2*j]);
|
|
}
|
|
|
|
for(int i=2*b+2; i<=l; i+=2)
|
|
{
|
|
int min;
|
|
int pos = (i>>1);
|
|
min = query(tree, 1, 1, l, pos-b, pos-a);
|
|
|
|
if (dp[i]<=inf) {
|
|
//if(dp[i]>min+1)
|
|
dp[i]=min+1;
|
|
updata(tree,1,1,l,pos,dp[i]);
|
|
/*for(int j=a; j<=b; j++) {
|
|
int idx = i-2*j;
|
|
if(idx<0) break;
|
|
if ( dp[i]>dp[idx]+1 ) dp[i]=dp[idx]+1;
|
|
}*/
|
|
}
|
|
}
|
|
if(dp[l]>=inf) return -1;
|
|
else return dp[l];
|
|
}
|
|
|
|
int main()
|
|
{
|
|
while (scanf("%d%d", &n, &l)!=EOF) {
|
|
|
|
scanf("%d%d", &a, &b);
|
|
inf = (l/a)+9;
|
|
for(int i=0; i<=l; i++) dp[i]=inf;
|
|
|
|
for(int i=0; i<n; i++) {
|
|
int s, e;
|
|
scanf("%d%d", &s, &e);
|
|
for(int j=s+1; j<e; j++) dp[j] = inf+1;
|
|
}
|
|
|
|
if(l&1==1) printf("-1\n");
|
|
printf("%d\n", dpro());
|
|
}
|
|
return 0;
|
|
}
|