new file: P17539.cpp

P17539.cpp

@@ -0,0 +1,28 @@
+#include <bits/stdc++.h>
+using namespace std;
+int pre[2000005];
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+    int n, m;
+    cin >> n >> m;
+    string s;
+    cin >> s;
+    for (int i = 0; i < n; ++i)
+        pre[i + 1] = pre[i] + (s[i] == '1');
+    int ans = 0;
+    for (int i = 0; i < m; ++i) {
+        int l, r;
+        cin >> l >> r;
+        int len = r - l + 1;
+        if (len % 2 != 0) {
+            cout << -1 << '\n';
+            return 0;
+        }
+        int c = pre[r] - pre[l - 1];
+        if (c != len / 2)
+            ++ans;
+    }
+    cout << (ans + 1) / 2 << '\n';
+    return 0;
+}