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class Solution {
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 public:
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  int twoCitySchedCost(vector<vector<int>> &costs) {
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    sort(costs.begin(), costs.end(),
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         [](const vector<int> &curr,
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            const vector<int> &next) { // CUSTOM COMPARATOR
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           return (curr[0] - curr[1]) <
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                  (next[0] - next[1]); // (comparing cost of sending to A - cost to B)
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         });
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    // original:   [[10,20],[30,200],[400,50],[30,20]]
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    // after sort: [[30,200],[10,20],[30,20],[400,50]]
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    // to do:         a       a          b         b
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    int sum = 0;
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    for (int i = 0; i < costs.size() / 2; i++) {
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      sum += costs[i][0];
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      // cout<<costs[i][0]<<" "; // 30 10
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    }
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    for (int i = costs.size() / 2; i < costs.size(); i++) {
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      sum += costs[i][1];
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      // cout<<costs[i][1]<<" "; // 20 50
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    }
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    return sum;
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  }
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};