其实这道题不是很难，不难想到f[i]表示覆盖到[0,i]的最少喷头数
很明显是一个dp+单调队列的问题
但是细节问题比较多，首先是不能覆盖到[0,l]外面，所以长度为奇数不能被完全覆盖
还有一些区间[bi,ei]只能被一个喷头覆盖，这意味着[0,s],bi<s<ei也是不能被完全覆盖的
标记一下就好了
最后注意判断一下是否可行
1 const inf=100000007; 2 type node=record 3 x,y:longint; 4 end; 5 var f,q:array[0..1000010] of longint; 6 can:array[0..1000010] of boolean; 7 a,b:array[0..1010] of longint; 8 p,n,l,w,v,i,j,h,t,ans:longint; 9 10 procedure sort(l,r: longint); 11 var i,j,x,y: longint; 12 begin 13 i:=l; 14 j:=r; 15 x:=a[(l+r) shr 1]; 16 repeat 17 while a[i]<x do inc(i); 18 while x<a[j] do dec(j); 19 if not(i>j) then 20 begin 21 swap(a[i],a[j]); 22 swap(b[i],b[j]); 23 inc(i); 24 j:=j-1; 25 end; 26 until i>j; 27 if l<j then sort(l,j); 28 if i<r then sort(i,r); 29 end; 30 31 procedure merge; 32 var l,r:longint; 33 begin 34 l:=a[1]; 35 r:=b[1]; 36 t:=0; 37 for i:=2 to n do 38 begin 39 if a[i]<r then r:=max(r,b[i]) 40 else begin 41 if r-l>v*2 then 42 begin 43 writeln(-1); 44 halt; 45 end; 46 inc(t); 47 a[t]:=l; 48 b[t]:=r; 49 l:=a[i]; 50 r:=b[i]; 51 end; 52 end; 53 if r-l>v*2 then 54 begin 55 writeln(-1); 56 halt; 57 end; 58 inc(t); 59 a[t]:=l; 60 b[t]:=r; 61 end; 62 63 begin 64 readln(n,l); 65 readln(w,v); 66 for i:=1 to n do 67 readln(a[i],b[i]); 68 sort(1,n); 69 merge; 70 for i:=1 to t do 71 for j:=a[i]+1 to b[i]-1 do 72 can[j]:=true; 73 f[0]:=0; 74 h:=1; 75 t:=1; 76 for i:=1 to l do 77 begin 78 f[i]:=inf; 79 p:=i-2*w; 80 if (p>=0) then 81 begin 82 while (t>1) and (h<t) and (f[q[t-1]]>=f[p]) do dec(t); 83 if not can[p] then 84 begin 85 q[t]:=p; 86 inc(t); 87 end; 88 end; 89 if (can[i]) or (i mod 2=1) then continue; 90 while (h<t) and (q[h]<i-2*v) do inc(h); 91 if (h<t) then f[i]:=f[q[h]]+1; 92 end; 93 if f[l]>=inf then writeln(-1) else writeln(f[l]); 94 end. 95 const inf=100000007; 96 type node=record 97 x,y:longint; 98 end; 99 var f,q:array[0..1000010] of longint; 100 can:array[0..1000010] of boolean; 101 a,b:array[0..1010] of longint; 102 p,n,l,w,v,i,j,h,t,ans:longint; 103 104 procedure sort(l,r: longint); 105 var i,j,x,y: longint; 106 begin 107 i:=l; 108 j:=r; 109 x:=a[(l+r) shr 1]; 110 repeat 111 while a[i]<x do inc(i); 112 while x<a[j] do dec(j); 113 if not(i>j) then 114 begin 115 swap(a[i],a[j]); 116 swap(b[i],b[j]); 117 inc(i); 118 j:=j-1; 119 end; 120 until i>j; 121 if l<j then sort(l,j); 122 if i<r then sort(i,r); 123 end; 124 125 procedure merge; 126 var l,r:longint; 127 begin 128 l:=a[1]; 129 r:=b[1]; 130 t:=0; 131 for i:=2 to n do 132 begin 133 if a[i]<r then r:=max(r,b[i]) 134 else begin 135 if r-l>v*2 then 136 begin 137 writeln(-1); 138 halt; 139 end; 140 inc(t); 141 a[t]:=l; 142 b[t]:=r; 143 l:=a[i]; 144 r:=b[i]; 145 end; 146 end; 147 if r-l>v*2 then 148 begin 149 writeln(-1); 150 halt; 151 end; 152 inc(t); 153 a[t]:=l; 154 b[t]:=r; 155 end; 156 157 begin 158 readln(n,l); 159 readln(w,v); 160 for i:=1 to n do 161 readln(a[i],b[i]); 162 sort(1,n); 163 merge; 164 for i:=1 to t do 165 for j:=a[i]+1 to b[i]-1 do 166 can[j]:=true; 167 f[0]:=0; 168 h:=1; 169 t:=1; 170 for i:=1 to l do 171 begin 172 f[i]:=inf; 173 p:=i-2*w; 174 if (p>=0) then 175 begin 176 while (t>1) and (h<t) and (f[q[t-1]]>=f[p]) do dec(t); 177 if not can[p] then 178 begin 179 q[t]:=p; 180 inc(t); 181 end; 182 end; 183 if (can[i]) or (i mod 2=1) then continue; 184 while (h<t) and (q[h]<i-2*v) do inc(h); 185 if (h<t) then f[i]:=f[q[h]]+1; 186 end; 187 if f[l]>=inf then writeln(-1) else writeln(f[l]); 188 end.