1137-n-th-tribonacci-number

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DevGod needs to write an editorial for this problem!

c

int tribonacci(int n){
    int arr[38];
    arr[0] = 0;
    arr[1] = 1;
    arr[2] = 1;
    arr[3] = 2;
    arr[4] = 4;

    for(int I = 5; I<=n; I++){
        arr[I] = arr[I-1]+arr[I-2]+arr[I-3];
    }

    return arr[n];
}

js

/**
 * @param {number} n
 * @return {number}
 */

var memo = {}
var tribonacci = function(n) {
    if(n == 0){return 0;}
    if(n == 1 || n == 2){return 1;}
    if(memo[n-1] === undefined){
        memo[n-1] = tribonacci(n-1);
    }
    if(memo[n-2] === undefined){
        memo[n-2] = tribonacci(n-2);
    }
    if(memo[n-3] === undefined){
        memo[n-3] = tribonacci(n-3);
    }
    return memo[n-1]+memo[n-2]+memo[n-3];
};