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N-th Tribonacci Number

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Lines changed: 29 additions & 9 deletions

Original file line number	Diff line number	Diff line change
`@@ -23,13 +23,33 @@`
`23`	`23`	`"""`
`24`	`24`	`class Solution:`
`25`	`25`	`def tribonacci(self, n: int) -> int:`
`26`		`- if n ==0:`
`27`		`- return 0`
`28`		`- elif n == 1orn==2:`
	`26`	`+ if n <=1:`
	`27`	`+ return n`
	`28`	`+ elif n == 2:`
`29`	`29`	`return 1`
`30`		`- a = 0`
`31`		`- b = c = 1`
`32`		`- for i in range(2,n):`
`33`		`- ans = a+b+c`
`34`		`- a,b,c = b,c,ans`
`35`		`- return ans`
	`30`	`+`
	`31`	`+ first, second, third = 0, 1, 1`
	`32`	`+ for _ in range(3, n+1):`
	`33`	`+ first, second, third = second, third, first + second + third`
	`34`	`+`
	`35`	`+ return third`
	`36`	`+`
	`37`	`+`
	`38`	`+class Solution1:`
	`39`	`+ def tribonacci(self, n: int) -> int:`
	`40`	`+ return self.helper(n, {0:0, 1:1, 2:1})`
	`41`	`+`
	`42`	`+ def helper(self, n, memo):`
	`43`	`+ if n not in memo:`
	`44`	`+ memo[n] = self.helper(n-1, memo) + self.helper(n-2, memo) + self.helper(n-3, memo)`
	`45`	`+ return memo[n]`
	`46`	`+`
	`47`	`+`
	`48`	`+# TLE`
	`49`	`+class Solution2:`
	`50`	`+ def tribonacci(self, n: int) -> int:`
	`51`	`+ if n <= 1:`
	`52`	`+ return n`
	`53`	`+ elif n == 2:`
	`54`	`+ return 1`
	`55`	`+ return self.tribonacci(n-1) + self.tribonacci(n-2) + self.tribonacci(n-3)`

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