LeetCode/TypeScript/3637.ts

// 3637. Trionic Array I


function isTrionic(nums: number[]): boolean {
    if ( nums.length < 4 ) { return false }

    function isIncreasing(s, e: number): boolean {
        let i: number = s
        while ( i < e ) { if ( nums[i] >= nums[i+1] ) { return false } i++ }
        return true
    }

    function isDecreasing(s, e: number): boolean {
        let i: number = s
        while ( i < e ) { if ( nums[i] <= nums[i+1] ) { return false } i++ }
        return true
    }

    let p: number = 1
    let q: number = 2
    let nlen: number = nums.length - 1

    while ( true ) {
        if ( isIncreasing(0, p)
             && isDecreasing(p, q)
             && isIncreasing(q, nlen) ) { return true }
        q++
        if ( q >= nlen ) {
            p++
            q = p+1
            if ( q >= nlen ) { return false }
        }
    }

    return false
};

function main() {
    function r(n: number[]) { console.log(`[${n}] = ${isTrionic(n)}`) }
    r([1,3,5,4,2,6])
    r([2,1,3])
    r([1,2,1,2])
}

main()