Leetcode #22 Generate Parenthesis updated November 2022

leetcode22-november22.ts

function nextPermutation(previousPermutations: string[][]): string[] {
    const nextPermutationsLength = previousPermutations.length;
    let nextPermutations = [];
    for (let i = 0; i < nextPermutationsLength; i++) {
        // each of the previous permutations becomes our "inner" permutations (array)
        const innerPermutations = previousPermutations[i];
        
        // calculate how many outer permutations we need based on where we are in the loop
        const outerPermutationsLength = nextPermutationsLength - 1 - i; 
        
        // grab from that position to get "outer permutations"
        const outerPermutations = previousPermutations[outerPermutationsLength];
        
        //  now that we have the outer permutations, step through them...
        let newPermutations = outerPermutations.flatMap(outer => innerPermutations.map(inner => `(${inner})${outer}`));
        newPermutations.forEach((newPerm) => {
            nextPermutations.push(newPerm);
        })
    }
    
    return nextPermutations;
}

function generateParenthesis(n: number): string[] {
    let result = [[""]];
    
    for (let i = 1; i < n+1; i++) {
        // push the array of new permutations into the result array 
        result.push(nextPermutation(result));
    }
    
    // result[n] now holds the array we need... 
    return result[n];
};