/*
 * @lc app=leetcode id=134 lang=java
 *
 * [134] Gas Station
 */

// @lc code=start
class Solution {
    /**
     * 本题核心为：若从i开始，计算到j时发现不行，那么从(i, j]范围内任一站点开始也不行，易进行论证
     * 
     * @param gas
     * @param cost
     * @return
     */
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start = 0, sum = 0, curIdx = 0;
        while(start < gas.length) {
            if(curIdx - start == gas.length) {
                return start;
            }
            int pos = curIdx % gas.length;
            if(sum + gas[pos] - cost[pos] < 0) {
                curIdx++;
                start = curIdx;
                sum = 0;
            } else {
                sum += gas[pos] - cost[pos];
                curIdx++;
            }
        }
        return -1;
    }
}
// @lc code=end