Number of Increasing Paths in a Grid LeetCode solution in C++

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class Solution {
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 public:
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  int mod = 1000000007;
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  int dx[4] = {1, 0, -1, 0};
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  int dy[4] = {0, 1, 0, -1};
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  int countPaths(vector<vector<int>> &grid) {
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    vector<vector<int>> dp(grid.size(), vector<int>(grid[0].size(), -1));
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    long long count = 0;
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    for (int i = 0; i < grid.size(); i++) {
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      for (int j = 0; j < grid[0].size(); j++) {
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        count = (count % mod + dfs(i, j, grid, dp) % mod) % mod;
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      }
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    }
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    return (int)count % mod;
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  }
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 protected:
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  bool isvalid(int x, int y, vector<vector<int>> &grid) {
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    if (x < 0 or x >= grid.size() or y < 0 or y >= grid[0].size()) return false;
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    return true;
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  }
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  int dfs(int x, int y, vector<vector<int>> &grid, vector<vector<int>> &dp) {
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    if (dp[x][y] != -1) return dp[x][y];
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    int ans = 1;
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    for (int i = 0; i < 4; i++) {
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      if (isvalid(x + dx[i], y + dy[i], grid) and grid[x][y] > grid[x + dx[i]][y + dy[i]]) {
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        ans = (ans % mod + dfs(x + dx[i], y + dy[i], grid, dp) % mod) % mod;
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      }
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    }
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    return dp[x][y] = ans % mod;
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  }
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};