Rename a variable to avoid confusion

Author: MiSawa

atcoder/mincostflow.hpp

@@ -122,7 +122,7 @@ template <class Cap, class Cost> struct mcf_graph {
             return true;
         };
         Cap flow = 0;
-        Cost cost = 0, prev_cost = -1;
+        Cost cost = 0, prev_cost_per_flow = -1;
         std::vector<std::pair<Cap, Cost>> result;
         result.push_back({flow, cost});
         while (flow < flow_limit) {
@@ -139,11 +139,11 @@ template <class Cap, class Cost> struct mcf_graph {
             Cost d = -dual[s];
             flow += c;
             cost += c * d;
-            if (prev_cost == d) {
+            if (prev_cost_per_flow == d) {
                 result.pop_back();
             }
             result.push_back({flow, cost});
-            prev_cost = d;
+            prev_cost_per_flow = d;
         }
         return result;
     }