Queue

Author: Adam Lin

645_predictPartyVictory.cpp

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+class Solution {
+public:
+    string predictPartyVictory(string senate) {
+        // Queues to store the indices of each senator from Radiant (R) and Dire (D)
+        queue<int> rad, dir;
+
+        // Get the total number of senators
+        int n = senate.length();
+
+        // Loop through the senate string to separate Radiant and Dire senators into different queues
+        for (int i = 0; i < n; i++) {
+            if (senate[i] == 'R') {
+                // If senator belongs to Radiant party, add their index to rad queue
+                rad.push(i);
+            } else {
+                // If senator belongs to Dire party, add their index to dir queue
+                dir.push(i);
+            }
+        }
+
+        // Diagram illustrating initial queue states:
+        // Senate: "RRDD"
+        // Radiant Queue (R): [0, 1]
+        // Dire Queue    (D): [2, 3]
+
+        /*
+            Initial queue states:
+            Radiant Queue (R): [0, 3]
+            Dire Queue    (D): [1, 2]
+
+            Step 1:
+            R0 vs D1: R0 bans D1
+            Radiant Queue (R): [3, 4]
+            Dire Queue    (D): [2]
+
+            Step 2:
+            R3 vs D2: D2 bans R3
+            Radiant Queue (R): [4]
+            Dire Queue    (D): []
+
+            Final state:
+            Winner: Radiant
+        */
+
+        // Process the queues while both parties still have senators left
+        while (!rad.empty() && !dir.empty()) {
+            // Compare the front senators from each party
+            if (rad.front() < dir.front()) {
+                // If the Radiant senator appears before the Dire senator, ban the Dire senator
+                // Push the Radiant senator to the back of the queue with updated index (n++)
+                rad.push(n++);
+            } else {
+                // Otherwise, the Dire senator bans the Radiant senator and pushes itself to the back
+                dir.push(n++);
+            }
+            // Remove the processed senators from the front of their respective queues
+            rad.pop();
+            dir.pop();
+        }
+
+        // Return the winning party based on which queue is not empty
+        return (rad.empty()) ? ("Dire") : ("Radiant");
+    }
+};