[leetcode#270] Closest Binary Search Tree Value

problem:

Given a non-empty binary search tree and a target value, find the value in the BST that's closest to the target.

Note:

• Given target value is a floating point.
• Guaranteed to has only one unique value in the BST, which is closest to the target.

Wrong solution 1:

 Public classSolution { Public intClosestvalue (TreeNode root,Doubletarget) {        if(Root = =NULL)            Throw NewIllegalArgumentException ("Root is null"); intClosest_gap =Integer.max_value; intret;  while(Root! =NULL) {            if(Math.Abs (Target-root.val) <closest_gap) {Closest_gap= Math.Abs (Target-root.val); RET=Root.val; }            if(target = =root.val)returnRoot.val; Else if(Target <root.val) Root=Root.left; ElseRoot=Root.right; }        returnret; }}

MistakesAnalysis:

Line 18:error:incompatible types:possible lossy conversion fromDoubleToint Line55: error:variable ret might not has been initializedmistake1: Even the problem has emphasized-a, a floating type, the Val in node is Integer type. I still blindly ignore the fact that:the type used forRecording the distance should be afloattype rather than Integer. Otherwise, we could lose precision. Case:target= 0.3Val_1:-1, Val_2:1(int) (Target-val_1) = 1;(int) (target-val_2) = 1; Wrong Fix:DoubleClosest_gap =Integer.max_value, .....if(Target-(Math.Abs) (Double) Root.val) <closest_gap) {Closest_gap= Math.Abs (Target-(Double) root.val); RET=Root.val;} ... Mistake2: Since"RET" is areturnValue, and it is solely enclosed inif-ElseBlocks, we must initialize it.

Wrong Solution 2:

 Public classSolution { Public intClosestvalue (TreeNode root,Doubletarget) {        if(Root = =NULL)            Throw NewIllegalArgumentException ("Root is null"); DoubleClosest_gap =Integer.max_value; intRET = 0;  while(Root! =NULL) {            if(Target-(Math.Abs) (Double) root.val) <=closest_gap) {Closest_gap= Math.Abs (Target-(Double) root.val); RET=Root.val; }            if(target = =root.val)returnRoot.val; Else if(Target <root.val) Root=Root.left; ElseRoot=Root.right; }        returnret; }}

MistakesAnalysis:

Error cases:[1500000000,1400000000], -1500000000.0Output:0expected:1400000000   Double, I still fail to consider the A floating point "target" could has larger range than Integer, WH Ich would produce the distance larger than "Integer.max_value". double closest_gap = integer.max_value; Fix:double closest_gap = Double.max_value;

Skill:

Finally, we get it right!!! But ThisA good lesson forus to learn a important skill:avoiding overflow through the advanced primitive types. Actually, we have meet it many times:reverse Integer, convert String into integer.we know:whether"Add" or "minus", we could easily exceed the operand ' s value range.Take the Integer as Example:integer. Max_value+ 1Overflow;integer. Min_value-1overflow; Even the operation between Integer with Double could easily result in overflow problem. Double.max_value+ 1overflow;double. Min_value-1overflow. Thus We have the take advantage of the advanced type!!!for the operations among Integer, we useLongTo hold the result.Longres = integer1 + integer 2. for ThisProblem, we were guaranteed, the target is a single floating point, it means we can use "double" to handle the result. <or forThe maximum comparision>note:closestvalue (TreeNode root,DoubleTarget) is a little misleading, but it's indeed a single floating point.

Solution:

 Public classSolution { Public intClosestvalue (TreeNode root,Doubletarget) {        if(Root = =NULL)            Throw NewIllegalArgumentException ("Root is null"); DoubleClosest_gap =Double.max_value; intRET = 0;  while(Root! =NULL) {            if(Target-(Math.Abs) (Double) root.val) <=closest_gap) {Closest_gap= Math.Abs (Target-(Double) root.val); RET=Root.val; }            if(target = =root.val)returnRoot.val; Else if(Target <root.val) Root=Root.left; ElseRoot=Root.right; }        returnret; }}

[leetcode#270] Closest Binary Search Tree Value