https://leetcode.com/problems/non-overlapping-intervals/

nonOverlappingIntervals.js

/**
 * @param {number[][]} intervals
 * @return {number}
 */
var eraseOverlapIntervals = function(intervals) {
    
    intervals.sort((a, b) => a[0] - b[0]); // asc by start time
    
    let [result, slow, fast] = [0, 0, 1];
    
    while(fast < intervals.length){
        
        let [s, f] = [intervals[slow], intervals[fast]];
        
        if(s[1] > f[0] && f[1] > s[0]){ // overlaps
            
            result++; // count a deletion
            
            if(intervals[slow][1] <= intervals[fast][1]){
                // delete the fast one
                fast++;
            }else{
                // delete the slow one
                slow = fast;
                fast++;
            }
        }else{ // no overlap
            slow = fast; // catch up the flow with the fast
            fast++; // and march the fast steadily on, one step ahead
        }
    }
    
    return result;
};