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Added Fibonacci index value problem

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Original file line number	Diff line number	Diff line change
`@@ -1330,6 +1330,42 @@ function fibonacci(n){`
`1330`	`1330`
`1331`	`1331`	`fibonacci(12); // 144`
`1332`	`1332`	```
	`1333`	`+### Find nth index value of fibonacci`
	`1334`	`+Given a number N return the index value of the Fibonacci sequence, where the sequence is:`
	`1335`	+```
	`1336`	`+1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ...`
	`1337`	+```
	`1338`	`+The solution is:`
	`1339`	+```
	`1340`	`+function fib(n){`
	`1341`	`+ var x = 0;`
	`1342`	`+ var y = 1;`
	`1343`	`+ if(n <= 2){`
	`1344`	`+ return n-1;`
	`1345`	`+ }`
	`1346`	`+ for(var i = 0; i < n; i++){`
	`1347`	`+ var tempY = y;`
	`1348`	`+ y = tempY + x;`
	`1349`	`+ x = tempY;`
	`1350`	`+`
	`1351`	`+ }`
	`1352`	`+ return y;`
	`1353`	`+}`
	`1354`	`+`
	`1355`	`+fib(4)`
	`1356`	`+// 5`
	`1357`	+```
	`1358`	`+To better performance, we can use memoization.`
	`1359`	+```
	`1360`	`+function fib(num, memo) {`
	`1361`	`+ memo = memo \|\| {};`
	`1362`	`+`
	`1363`	`+ if (memo[num]) return memo[num];`
	`1364`	`+ if (num <= 1) return 1;`
	`1365`	`+`
	`1366`	`+ return memo[num] = fib(num - 1, memo) + fib(num - 2, memo);`
	`1367`	`+}`
	`1368`	+```
`1333`	`1369`	`### Find Greatest Common Divisor`
`1334`	`1370`	`Using Euclidean algorithm:`
`1335`	`1371`	```

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