772. 只出现一次的字符

https://www.acwing.com/problem/content/submission/code_detail/6847872/

AcWing/772/772.cpp

@@ -0,0 +1,33 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int main() {
+    string s;
+    vector<char> ans;
+    int a = -1;
+    char c = 'a';
+    cin >> s;
+    map<char, int> m, m1;
+    for (int i = 0; i < s.size(); i++) {
+        m[s[i]]++;
+        if (!m1.count(s[i])) m1[s[i]] = i;
+    }
+    for (char i = 'a'; i <= 'z'; i++) {
+        if (m[i] == 1) {
+            ans.push_back(i);
+        }
+    }
+    if (ans.empty()) {
+        cout << "no" << endl;
+    } else {
+        for (char i : ans) {
+            if (a == -1 || m1[i] < a) {
+                a = m1[i];
+                c = i;
+            }
+        }
+        cout << c << endl;
+    }
+    return 0;
+}