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algorithm: first unique char in a string (TheAlgorithms#1103)

* feat: Added Algo first unique char in a string.* Optimised algo to linear time complexity* removed double quotes* Review changes: if-else logic

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Original file line number	Diff line number	Diff line change
`@@ -299,6 +299,7 @@`
`299`	`299`	`*[CountVowels](String/CountVowels.js)`
`300`	`300`	`*[CreatePermutations](String/CreatePermutations.js)`
`301`	`301`	`*[DiceCoefficient](String/DiceCoefficient.js)`
	`302`	`+*[FirstUniqueCharacter](String/FirstUniqueCharacter.js)`
`302`	`303`	`*[FormatPhoneNumber](String/FormatPhoneNumber.js)`
`303`	`304`	`*[GenerateGUID](String/GenerateGUID.js)`
`304`	`305`	`*[HammingDistance](String/HammingDistance.js)`

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`@@ -0,0 +1,30 @@`
	`1`	`+/**`
	`2`	`+ *@function firstUniqChar`
	`3`	`+ *@description Given a string str, find the first non-repeating character in it and return its index. If it does not exist, return -1.`
	`4`	`+ *@param {String} str - The input string`
	`5`	`+ *@return {Number} - The index of first unique character.`
	`6`	`+ *@example firstUniqChar("javascript") => 0`
	`7`	`+ *@example firstUniqChar("sesquipedalian") => 3`
	`8`	`+ *@example firstUniqChar("aabb") => -1`
	`9`	`+ */`
	`10`	`+`
	`11`	`+constfirstUniqChar=(str)=>{`
	`12`	`+if(typeofstr!=='string'){`
	`13`	`+thrownewTypeError('Argument should be string')`
	`14`	`+}`
	`15`	`+constcount=newMap()`
	`16`	`+`
	`17`	`+for(constcharofstr){`
	`18`	`+if(!count[char]){`
	`19`	`+count[char]=1`
	`20`	`+}else{`
	`21`	`+count[char]++`
	`22`	`+}`
	`23`	`+}`
	`24`	`+for(leti=0;i<str.length;i++){`
	`25`	`+if(count[str[i]]===1)returni`
	`26`	`+}`
	`27`	`+return-1`
	`28`	`+}`
	`29`	`+`
	`30`	`+export{firstUniqChar}`

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	`1`	`+import{firstUniqChar}from'../FirstUniqueCharacter'`
	`2`	`+`
	`3`	`+describe('firstUniqChar',()=>{`
	`4`	`+it('locates the index of first unique character in the string',()=>{`
	`5`	`+expect(firstUniqChar('javascript')).toEqual(0)`
	`6`	`+expect(firstUniqChar('sesquipedalian')).toEqual(3)`
	`7`	`+expect(firstUniqChar('aabb')).toEqual(-1)`
	`8`	`+})`
	`9`	`+})`

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