Map of Highest Peak LeetCode solution in C++

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class Solution {
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 public:
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  vector<vector<int>> highestPeak(vector<vector<int>> &isWater) {
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    int r = isWater.size();
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    int c = isWater[0].size();
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    queue<pair<int, int>> curr;
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    for (int i = 0; i < r; i++) {
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      for (int j = 0; j < c; j++) {
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        // set the land cell to -1 (not visited)
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        if (isWater[i][j] == 0) {
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          isWater[i][j] = -1;
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        }
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        // set the water cell to zero and to queue
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        else {
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          isWater[i][j] = 0;
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          curr.push({i, j});
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        }
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      }
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    }
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    int hill = 0;
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    while (!curr.empty()) {
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      int len = curr.size();
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      for (int k = 0; k < len; k++) {
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        // for each cell check its 4 boundary cells
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        // if it is not visited, increase its hill by 1
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        pair<int, int> fnt = curr.front();
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        curr.pop();
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        int i = fnt.first, j = fnt.second;
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        // top cell
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        if (i > 0 && isWater[i - 1][j] == -1) {
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          isWater[i - 1][j] = hill + 1;
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          curr.push({i - 1, j});
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        }
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        // bottom cell
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        if ((i < r - 1) && (isWater[i + 1][j] == -1)) {
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          isWater[i + 1][j] = hill + 1;
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          curr.push({i + 1, j});
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        }
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        // left cell
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        if (j > 0 && (isWater[i][j - 1] == -1)) {
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          isWater[i][j - 1] = hill + 1;
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          curr.push({i, j - 1});
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        }
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        // right cell
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        if ((j < c - 1) && (isWater[i][j + 1] == -1)) {
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          isWater[i][j + 1] = hill + 1;
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          curr.push({i, j + 1});
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        }
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      }
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      // after 1 complete round increase the height of the hill
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      hill += 1;
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    }
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    return isWater;
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  }
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};