2

Author: kedebug

FirstMissingPositive/FirstMissingPositive.cpp

@@ -0,0 +1,62 @@
+class Solution {
+public:
+    int firstMissingPositive(int A[], int n) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        int i = 0;
+        while (i < n) {
+            if (A[i] != i + 1 && 0 < A[i] && A[i] <= n && A[A[i]-1] != A[i])
+                swap(A[i], A[A[i]-1]);
+            else
+                i += 1;
+        }
+        int first_positive = 0;
+        for (int i = 0; i < n; i++) {
+            if (A[i] != i + 1) {
+                first_positive = i + 1;
+                break;
+            }
+        }
+        if (first_positive == 0)
+            first_positive = n + 1;
+        return first_positive;
+    }
+};
+
+//
+// solution 2
+//
+class Solution {
+public:
+    int firstMissingPositive(int A[], int n) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        bool find_1 = false;
+        for (int i = 0; i < n; i++) {
+            if (A[i] == 1)
+                find_1 = true;
+            else if (A[i] <= 0)
+                A[i] = 1;
+        }
+        if (!find_1) return 1;
+        for (int i = 0; i < n; i++) {
+            if (A[i] > 0 && A[i] <= n && A[A[i]-1] > 0) {
+                A[A[i]-1] = -A[A[i]-1];
+            }
+            else if (A[i] <= -1 && -A[i] <= n && A[-A[i]-1] > 0)
+                A[-A[i]-1] = -A[-A[i]-1];
+        }
+        int first_positive = 0;
+        for (int i = 0; i < n; i++) {
+            if (A[i] > 0) {
+                first_positive = i + 1;
+                break;
+            }
+        }
+        if (first_positive == 0)
+            first_positive = n + 1;
+        return first_positive;
+    }
+};