leetcode- Largest Rectangle In Histogram

/**
 * @param {number[]} heights
 * @return {number}
 */
var largestRectangleArea = function(heights) {
    let h = 1;
    // let max = heights.reduce((r, item)=>Math.max(r, item), 0);
    let m = new Set()
    // let m = [];
    heights.forEach(item => m.add(item));
    let curAns = 0;
    
    for(let me of m){
        for(let i = 0; i < heights.length; i++){
            if(heights[i] >= me){
                let j = i+1;
                while(j < heights.length && heights[j] >= me) j++;
                // console.log(`${h}일때, ${i}부터 ${j}까지`)
                curAns = Math.max(curAns, (j-i)*me);
                i = j;
            }
        }
        
        h++;
    }
    
    return curAns;
};

/**
 * @param {number[]} heights
 * @return {number}
 */
var largestRectangleArea = function(heights) {
    let stack = [];
    
    let curAns = 0;
    heights.push(0);
    stack.push(0);
    
    for(let i = 1; i < heights.length; i++){
        while(heights[i] < heights[stack[stack.length-1]]){
            let idx = stack.pop();
            // console.log(`${heights[idx]} -> ${i},${idx}`)
            
            // i - stack[stack.length-1] - 1 : if there's still elements in stack,
            // it would means that it was small enough to not get popped which means,
            // it can't be bigger than 'curHeight'.
            // i : is when stack is empty.
            
            // good example case for this would be, [2,1,6,5,2,3] => ans: 10
            let curHeight = heights[idx];
            let curWidth = stack.length? i - stack[stack.length-1] - 1 : i;
            curAns = Math.max(curHeight * curWidth, curAns);
        }
        stack.push(i);
    }
    
    return curAns;
};