<p>Given a 2D array of characters <code>grid</code> of size <code>m x n</code>, you need to find if there exists any cycle consisting of the <strong>same value</strong> in <code>grid</code>.</p>

<p>A cycle is a path of <strong>length 4 or more</strong> in the grid that starts and ends at the same cell. From a given cell, you can move to one of the cells adjacent to it - in one of the four directions (up, down, left, or right), if it has the <strong>same value</strong> of the current cell.</p>

<p>Also, you cannot move to the cell that you visited in your last move. For example, the cycle <code>(1, 1) -&gt; (1, 2) -&gt; (1, 1)</code> is invalid because from <code>(1, 2)</code> we visited <code>(1, 1)</code> which was the last visited cell.</p>

<p>Return <code>true</code> if any cycle of the same value exists in <code>grid</code>, otherwise, return <code>false</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/07/15/1.png" style="width: 231px; height: 152px;" /></strong></p>

<pre>
<strong>Input:</strong> grid = [[&quot;a&quot;,&quot;a&quot;,&quot;a&quot;,&quot;a&quot;],[&quot;a&quot;,&quot;b&quot;,&quot;b&quot;,&quot;a&quot;],[&quot;a&quot;,&quot;b&quot;,&quot;b&quot;,&quot;a&quot;],[&quot;a&quot;,&quot;a&quot;,&quot;a&quot;,&quot;a&quot;]]
<strong>Output:</strong> true
<strong>Explanation: </strong>There are two valid cycles shown in different colors in the image below:
<img alt="" src="https://assets.leetcode.com/uploads/2020/07/15/11.png" style="width: 225px; height: 163px;" />
</pre>

<p><strong class="example">Example 2:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/07/15/22.png" style="width: 236px; height: 154px;" /></strong></p>

<pre>
<strong>Input:</strong> grid = [[&quot;c&quot;,&quot;c&quot;,&quot;c&quot;,&quot;a&quot;],[&quot;c&quot;,&quot;d&quot;,&quot;c&quot;,&quot;c&quot;],[&quot;c&quot;,&quot;c&quot;,&quot;e&quot;,&quot;c&quot;],[&quot;f&quot;,&quot;c&quot;,&quot;c&quot;,&quot;c&quot;]]
<strong>Output:</strong> true
<strong>Explanation: </strong>There is only one valid cycle highlighted in the image below:
<img alt="" src="https://assets.leetcode.com/uploads/2020/07/15/2.png" style="width: 229px; height: 157px;" />
</pre>

<p><strong class="example">Example 3:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/07/15/3.png" style="width: 183px; height: 120px;" /></strong></p>

<pre>
<strong>Input:</strong> grid = [[&quot;a&quot;,&quot;b&quot;,&quot;b&quot;],[&quot;b&quot;,&quot;z&quot;,&quot;b&quot;],[&quot;b&quot;,&quot;b&quot;,&quot;a&quot;]]
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 500</code></li>
	<li><code>grid</code> consists only of lowercase English letters.</li>
</ul>

class Solution {
    struct Pair{
        int i;
        int j;
    };

    bool helper(vector<vector<bool>>& used, vector<vector<char>>& grid, int i, int j){
        char cycle = grid[i][j];
        Pair starter;
        starter.i = i;
        starter.j = j;
        stack<Pair> toVisit;
        toVisit.push(starter);
        while(!toVisit.empty()){
            int painted = 0;
            Pair cur = toVisit.top();
            toVisit.pop();
            used[cur.i][cur.j] = true;
            if(cur.i - 1 >= 0){
                if(grid[cur.i - 1][cur.j] == cycle){
                    if(used[cur.i - 1][cur.j]){
                        painted++;
                    } else {
                        Pair newOne;
                        newOne.i = cur.i - 1;
                        newOne.j = cur.j;
                        toVisit.push(newOne);
                    }
                }
            }
            if(cur.i + 1 <= grid.size() - 1){
                if(grid[cur.i + 1][cur.j] == cycle){
                    if(used[cur.i + 1][cur.j]){
                        painted++;
                    } else {
                        Pair newOne;
                        newOne.i = cur.i + 1;
                        newOne.j = cur.j;
                        toVisit.push(newOne);
                    }
                }
            }
            if(cur.j - 1 >= 0){
                if(grid[cur.i][cur.j - 1] == cycle){
                    if(used[cur.i][cur.j - 1]){
                        painted++;
                    } else {
                        Pair newOne;
                        newOne.i = cur.i;
                        newOne.j = cur.j - 1;
                        toVisit.push(newOne);
                    }
                }
            }
            if(cur.j + 1 <= grid[0].size() - 1){
                if(grid[cur.i][cur.j + 1] == cycle){
                    if(used[cur.i][cur.j + 1]){
                        painted++;
                    } else {
                        Pair newOne;
                        newOne.i = cur.i;
                        newOne.j = cur.j + 1;
                        toVisit.push(newOne);
                    }
                }
            }

            if(painted >= 2){
                return true;
            }
        }
        return false;
    }

public:
    bool containsCycle(vector<vector<char>>& grid) {
        vector<vector<bool>> used(grid.size(), vector<bool>(grid[0].size(), false));
        for(int i = 0; i < grid.size(); i++){
            for(int j = 0; j < grid[0].size(); j++){
                if(!used[i][j]){
                    if(helper(used, grid, i, j)){
                        return true;
                    }
                }
            }
        }
        return false;
    }
};
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