[leetcode#163] Missing Ranges

problem:

Given a sorted integer array where the range of elements is [lower, Upper] inclusive, return its missin G Ranges.

For example, given [0, 1, 3, 50, 75] , lower = 0 and upper =, return["2", "4->49", "51->74", "76->99"].

General Analysis:

This kind problem are easy, it just test your proramming skills. Basic idea:according to the problem, the gap between and Numbers:nums[i], nums[i+1] should be recorded. There could be following situation:------------------------------------------------------------------------------------------------ Case1:no Gap (Nums[i] + 1 = = Nums[i+1]) We need to the record nothing.------------------------------------------------------------------------------------------------ Case2:the gap ' s length is 1. (Nums[i] + 2 = nums[i+1]) We need to record one number. Nums[i]+1.------------------------------------------------------------------------------------------------ Case3:the gap ' s length is larger than 1. (Nums[i] + 2 < nums[i+1]) We need to record the range. [Nums[i]+1, Nums[i+1]-1]. Write in ThisThe IS-a little ugly, what's more we had lower and upper must be included. We could use of variables for this purpose: (to compute the gap between nums[i-1] and Nums[i])--------------------------- ---------------------------------------------------------------------after:the number after nums[i-1]pre:the number before nums[i]------------------------------------------------------------------------------------------------if(Pre = =After ) Ret.add (pre+ "");Else if(Pre >After ) Ret.add ( after+ "+" +pre);= Nums[i] + 1; Skill:to involve the lower and upper, we could assign"After" with "lower" before scanning the nums. and assign "pre" with "upper"After the scan.intafter =Lower;intPre; for(inti = 0; i < nums.length; i++) {...} Pre=Upper;if(Pre = =After ) Ret.add (pre+ "");Else if(Pre >After ) Ret.add ( after+ "+" + Pre);

Wrong solution:

 Public classSolution { PublicList<string> Findmissingranges (int[] Nums,intLowerintUpper) {        if(Nums = =NULL)            Throw NewIllegalArgumentException ("Nums is null"); List<String> ret =NewArraylist<string> (); if(Nums.length = = 0) {String temp= lower + "+" +Upper;            Ret.add (temp); returnret; }        intafter =Lower; intPre;  for(inti = 0; i < nums.length; i++) {Pre= Nums[i]-1; if(Pre = =After ) Ret.add (pre+ ""); Else if(Pre >After ) Ret.add ( after+ "+" +pre); after= Nums[i] + 1; } Pre=Upper; if(Pre = =After ) Ret.add (pre+ ""); Else if(Pre >After ) Ret.add ( after+ "+" +pre); returnret; }}

MistakeAnalysis:

Error Case:[], 1, 1output:["1->1"]expected:["1"]mistake Analysis:i has failed to consdier the corner CaseWhen nums.length = 0, and lower and upper share the same value. Thus We should not use",". Fix:if(Lower <Upper) {String temp= lower + "+" +Upper; Ret.add (temp);} Else{ret.add (lower+ "");} Lesson:when the output should be genereated forDifferent format (like "Num1", "Num1-num2"), you should is careful with your handling with corner Case.

Solution:

 Public classSolution { PublicList<string> Findmissingranges (int[] Nums,intLowerintUpper) {        if(Nums = =NULL)            Throw NewIllegalArgumentException ("Nums is null"); List<String> ret =NewArraylist<string> (); if(Nums.length = = 0) {            if(Lower <Upper) {String temp= lower + "+" +Upper;            Ret.add (temp); } Else{ret.add (lower+ ""); }            returnret; }        intafter =Lower; intPre;  for(inti = 0; i < nums.length; i++) {Pre= Nums[i]-1; if(Pre = =After ) Ret.add (pre+ ""); Else if(Pre >After ) Ret.add ( after+ "+" +pre); after= Nums[i] + 1; } Pre=Upper; if(Pre = =After ) Ret.add (pre+ ""); Else if(Pre >After ) Ret.add ( after+ "+" +pre); returnret; }}

[leetcode#163] Missing Ranges