Mathematica, 197 193 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n},Reverse@#2]&@@@Tuples[Subsets@Range[3,n=Length[i=FromDigits/@StringSplit@InputString[]]]-1,2],{}⋃#==Sort@#∧And@@Thread[i[[#]]≥Abs[#-Rest@#~Append~1]]&]]/.∞->-1

#Mathematica, ~~197~~ 193 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n},Reverse@#2]&@@@Tuples[Subsets@Range[3,n=Length[i=FromDigits/@StringSplit@InputString[]]]-1,2],{}⋃#==Sort@#∧And@@Thread[i[[#]]≥Abs[#-Rest@#~Append~1]]&]]/.∞->-1

Mathematica, 197 193 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n},Reverse@#2]&@@@Tuples[Subsets@Range[3,n=Length[i=FromDigits/@StringSplit@InputString[]]]-1,2],{}⋃#==Sort@#∧And@@Thread[i[[#]]≥Abs[#-Rest@#~Append~1]]&]]/.∞->-1

added 7 characters in body

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edited Oct 26, 2013 at 7:28

alephalpha

50k
7
68
182

#Mathematica, 197~~197~~ 193 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n+1n},Reverse@#2]&@@@Tuples[Subsets@Range[2Reverse@#2]&@@@Tuples[Subsets@Range[3,n=Length[i=FromDigits/@StringSplit@InputString[]]@StringSplit@InputString[]]]-1]1,2],{}⋃#==Sort@#&&And@@Thread[i[[#]]>=Abs[#⋃#==Sort@#∧And@@Thread[i[[#]]≥Abs[#-Rest@#~Append~1]]&]]/.∞->-1

#Mathematica, 197 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n+1},Reverse@#2]&@@@Tuples[Subsets@Range[2,n=Length[i=FromDigits/@StringSplit@InputString[]]-1],2],{}⋃#==Sort@#&&And@@Thread[i[[#]]>=Abs[#-Rest@#~Append~1]]&]]/.∞->-1

#Mathematica, ~~197~~ 193 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n},Reverse@#2]&@@@Tuples[Subsets@Range[3,n=Length[i=FromDigits/@StringSplit@InputString[]]]-1,2],{}⋃#==Sort@#∧And@@Thread[i[[#]]≥Abs[#-Rest@#~Append~1]]&]]/.∞->-1

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created Oct 22, 2013 at 9:29

alephalpha

50k
7
68
182

#Mathematica, 197 chars

Brute force.

Min[Length/@Select[Join[{1},#,{n+1},Reverse@#2]&@@@Tuples[Subsets@Range[2,n=Length[i=FromDigits/@StringSplit@InputString[]]-1],2],{}⋃#==Sort@#&&And@@Thread[i[[#]]>=Abs[#-Rest@#~Append~1]]&]]/.∞->-1

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Mathematica, 197 193 chars

Mathematica, 197 193 chars