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1137. N-th Tribonacci Number

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	`1`	`+/**`
	`2`	`+The tribonacci series is a generalization of the Fibonacci sequence where each term is the sum of the three preceding terms.`
	`3`	`+The Tribonacci Sequence:`
	`4`	`+0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513, 35890, 66012, 121415, 223317, 410744, 755476, 1389537, 2555757, 4700770, 8646064, 15902591, 29249425, 53798080, 98950096, 181997601, 334745777, 615693474, 1132436852... so on`
	`5`	`+General Form of Tribonacci number:`
	`6`	`+`
	`7`	`+`
	`8`	`+a(n) = a(n-1) + a(n-2) + a(n-3)`
	`9`	`+with`
	`10`	`+a(0) = a(1) = 0, a(2) = 1.`
	`11`	`+*/`
	`12`	`+class Solution {`
	`13`	`+ fun tribonacci(n: Int): Int {`
	`14`	`+ if(n == 0){`
	`15`	`+ return 0`
	`16`	`+ }`
	`17`	`+ if(n==1 \|\| n == 2) return 1`
	`18`	`+`
	`19`	`+ var a = 0 //T_0`
	`20`	`+ var b = 1 //T_1`
	`21`	`+ var c = 1 //T_2`
	`22`	`+`
	`23`	`+ for(i in 3..n){`
	`24`	`+ val next = a + b + c`
	`25`	`+ a = b`
	`26`	`+ b = c`
	`27`	`+ c = next`
	`28`	`+ }`
	`29`	`+ return c`
	`30`	`+ }`
	`31`	`+}`

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