First missing positive

Signed-off-by: Leo Ma <[email protected]>

041_first_missing_positive/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test missing_positive.c

041_first_missing_positive/missing_positive.c

@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+static void swap(int *a, int *b)
+{
+    int tmp = *a;
+    *a = *b;
+    *b = tmp;
+}
+
+static int firstMissingPositive(int* nums, int numsSize) {
+    if (numsSize < 1) {
+        return 1;
+    }
+
+    int i = 0;
+    while (i < numsSize) {
+        if (nums[i] != i + 1 && nums[i] > 0 && nums[i] <= numsSize && nums[i] != nums[nums[i] - 1]) {
+            swap(nums + i, nums + nums[i] - 1);
+        } else {
+            i++;
+        }
+    }
+
+    for (i = 0; i < numsSize; i++) {
+        if (nums[i] != i + 1) break;
+    }
+    return i + 1;
+}
+
+int main(int argc, char **argv)
+{
+    int i, count = argc - 1;
+    int *nums = malloc(count * sizeof(int));
+    for (i = 0; i < count; i++) {
+        nums[i] = atoi(argv[i + 1]);
+    }
+    printf("%d\n", firstMissingPositive(nums, count));
+    return 0;
+}