LeetCode gas station

gistfile1.txt

/**
 * @param {number[]} gas
 * @param {number[]} cost
 * @return {number}
 */
var canCompleteCircuit = function(gas, cost) {
    
        
        if(gas.length==0){
		return -1;
	}
			   	
	if(gas.length==1){
		return gas[0]-cost[0]<0?-1:0;
	}
			
		
	
	let start = 0;
	let end = 1;

	
	let curr= gas[0]-cost[0];

	
	while(start!=end) {
	
	     while(curr<0 && start!=end) {

	
		 curr= curr- (gas[start]-cost[start]);
		 start = (start+1)%gas.length;
	
		 if(start==0)
		    return -1;
	      }
	
	     curr+= gas[end]-cost[end];
	     end = (end+1)%gas.length;
	 }
	
	   if(curr<0)
	      return -1;
	
	   return start; 
    
};