There is something wrong with [1,1,-2,1,4]


  • 1
    S

    As the title above, [1,1,-2,1,4] has loop of 3->4->3->...,and it's a "forward" loop, but the "run code" returns false
    I think it's because I mix a "fake" loop 0->1->2->0 with a genuine loop.


  • 0
    M

    I agree with you. Here is my solution by marked the visited num to zero.
    I think we can start from any index of the array. If there exist a forward/backward loop in the array, we should return true.
    It's obvious that [1,1,-2,1,4] exist a forward loop 3 -> 4 -> 3.

       bool circularArrayLoop(vector<int>& nums) {
            if (nums.size() == 0) return false;
            int len = nums.size();
            for (int i = 0; i < nums.size(); i++) {
                if (nums[i] == 0) return false;
            }
            int pos = 0;
            bool fwd = nums[0] > 0, lst = true, ret = false;
            for (int i = 0; i < len; i++) {
                pos = i;
                if (nums[pos] == 0) continue;
                while (true) {
                    if (nums[pos] == 0) {
                        ret |= fwd && lst;
                        break;
                    }
                    int op = pos;
                    lst = fwd;
                    fwd = nums[pos] > 0;
                    pos = (pos + nums[pos] + len) % len;
                    if (pos == op) {
                        break;
                    }
                    nums[op] = 0;
                }
                if (ret) return ret;
            }
            
            return ret;
        }
    
    

  • 0
    A

    @MyPremiumAccount yeah even [1,2,5,-1,-2] returns false but there is a loop from 5 it jumps to 5 and so on..


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