minWindowSubstring.js

// Sliding window: TC: O(m) + O(n) SC: O(m) + O(n)

function minWindowSubstring(windowStr, subStr) {
    let windowStrCount = new Map();
    let subStrCount = new Map();

    let minLength = Number.MAX_VALUE;
    let leftIndex = rightIndex = -1;

    for(const ch of subStr) {
        subStrCount.set(ch, (subStrCount.get(ch) || 0) + 1);
    }

    let having = 0; required = subStrCount.size;
    let left = right = 0;

    for(right = 0; right < windowStr.length; right++) {
        let rightChar = windowStr.charAt(right);
        windowStrCount.set(rightChar, (windowStrCount.get(right) || 0) +1);
        if(subStrCount.has(rightChar) && subStrCount.get(rightChar) === windowStrCount.get(rightChar)) {
            having++;
        }

        while(required === having) {
            if(minLength > right-left+1) {
                minLength = right-left+1;
                leftIndex = left;
                rightIndex = right;
            }

            let leftChar = windowStr.charAt(left);
            windowStrCount.set(leftChar, windowStrCount.get(leftChar)-1);
            if(subStrCount.has(leftChar) && subStrCount.get(leftChar) > windowStrCount.get(leftChar)) {
                having--;
            }
            left++;
        }
    }
    if(leftIndex === -1 || rightIndex === -1) {
        return "";
    } else {
        return windowStr.substring(leftIndex, rightIndex+1);
    }

}

let s ="ADOBECODEBANC";
let t= "ABC";
console.log(minWindowSubstring(s, t));