Interviewbit Window String

minimumWindowString.js

module.exports = { 
	minWindow : function(A, B){
        const map = {};
        let missing = B.length;
        let fast=0, slow=0;
        let shortest = [0,Infinity];
        
        for(let i=0;i<B.length;i++){
            if(B[i] in map){
                map[B[i]].cnt += 1;  
            }else{
                map[B[i]] = {
                    cnt: 1,
                    value: 0
                };   
            }
        }
        
        
        for(fast=0;fast<A.length;fast++){
            if(A[fast] in map){
                if(map[A[fast]].value < map[A[fast]].cnt){
                    missing -= 1;
                }
                
                map[A[fast]].value += 1;
            }

            while(missing == 0){
                if( (fast - slow) < (shortest[1] - shortest[0])){
                    shortest[0] = slow;
                    shortest[1] = fast;
                }
                
                
                if(A[slow] in map){
                    map[A[slow]].value -=1;
                    if(map[A[slow]].value < map[A[slow]].cnt){
                        missing+=1;
                    }
                }
                
                
                slow++;
            }
        }

        return shortest[1] === Infinity ? "" : A.slice(shortest[0], shortest[1] + 1);
	}
};