[Positions] two pointers becomes gas station

The general idea:

It is probably the meaning of the questions: a ring N sites, each site can refuel gas [i], each site to its site next to consume cost [i], ask if you can find a starting point to be able to walk all the ring point (end == starting point)

The idea is, in fact, can be understood reach each site to increase gas [i] -cost [i], of course, this number might be negative, but we must ensure that the total number of oil sum> = 0. Set a start pointer and a pointer to end and then if coupled sum> = 0, then the end ++, otherwise start - (total since start ++ will only make oil less, only fallback start see if you can get a positive number of gas [i] on a stand - cost [i] to increase total oil). Until start == sum, and then determines whether the final sum> = 0, i.e., whether or solution.

I feel I have learned is that this has a beginning and end uncertain start and end points have questions, you can set two pointers , different operations on different circumstances design pointer. (Feet before borrowing is this idea)

AC Code:

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
        int start = gas.size()-1;
        int end = 0;
        int sum = gas[start] - cost[start];
        while(start>end)
        {
            if(sum>=0)
            {
                sum += gas[end] - cost[end];
                end++;
            }
            else 
            {
                start--;
                sum += gas[start] - cost[start];
            }
        }
        if(sum>=0)
            return start;
        else
            return -1;
    }
};

 

Guess you like

Origin blog.csdn.net/m0_38033475/article/details/92060134