From 5af36c7bcbfd94a865261adfda3360330ceaa781 Mon Sep 17 00:00:00 2001
From: Jidong Xiao <xiaoj8@rpi.edu>
Date: Sat, 11 Nov 2023 22:51:34 -0500
Subject: [PATCH] adding queue problem

---
 leetcode/p387_first_unique_char.cpp | 32 +++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 leetcode/p387_first_unique_char.cpp

diff --git a/leetcode/p387_first_unique_char.cpp b/leetcode/p387_first_unique_char.cpp
new file mode 100644
index 0000000..7e3ec7b
--- /dev/null
+++ b/leetcode/p387_first_unique_char.cpp
@@ -0,0 +1,32 @@
+class Solution {
+public:
+    int firstUniqChar(string s) {
+        int len = s.length();
+        std::unordered_map<char, int> map1;
+        // traverse the string and count the frequence of each character.
+        for(int i=0;i<len;i++){
+            map1[s[i]]++;
+        }
+	// push all characters in a queue.
+        std::queue<char> myQueue;
+        for(int i=0;i<len;i++){
+            myQueue.push(s[i]);
+        }
+        int index = 0;
+        while(!myQueue.empty()){
+		// if frequency is larger than 1, it's not what we want.
+            if(map1[myQueue.front()]>1){
+                myQueue.pop();
+                index++;
+            }else{
+                // found the non-repeating character
+                break;
+            }
+        }
+        // if not found, return -1.
+        if(index>=len){
+            return -1;
+        }
+        return index;
+    }
+};