# Self Crossing Problem

## Description

LeetCode Problem 335.

You are given an array of integers distance.

You start at point (0,0) on an X-Y plane and you move distance[0] meters to the north, then distance[1] meters to the west, distance[2] meters to the south, distance[3] meters to the east, and so on. In other words, after each move, your direction changes counter-clockwise.

Return true if your path crosses itself, and false if it does not.

Example 1:

``````1
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Input: distance = [2,1,1,2]
Output: true
``````

Example 2:

``````1
2
Input: distance = [1,2,3,4]
Output: false
``````

Example 3:

``````1
2
Input: distance = [1,1,1,1]
Output: true
``````

Constraints:

• 1 <=distance.length <= 10^5
• 1 <=distance[i] <= 10^5

## Sample C++ Code

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class Solution {
public:
bool isSelfCrossing(vector<int>& x) {
x.insert(x.begin(), 4, 0);

int len = x.size();
int i = 4;

// outer spiral
for (; i < len && x[i] > x[i - 2]; i++);

if (i == len) return false;

// check border
if (x[i] >= x[i - 2] - x[i - 4]) {
x[i - 1] -= x[i - 3];
}

// inner spiral
for (i++; i < len && x[i] < x[i - 2]; i++);

return i != len;
}
};
``````