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// 41. First Missing Positive
#include "leetcode.h"
/*
* given an unsorted integer array 'nums', return the smallest missing positive
* number. you must implement an algorithm that runs in O(n) time and uses O(1)
* auxiliary space.
*/
int firstMissingPositive(int *nums, int nums_size) {
int x = 0;
for (int i = 0; i < nums_size; i++)
if (nums[i] == 1) {
x = 1;
break;
}
if (!x)
return 1;
if (nums_size == 1)
return 2;
for (int i = 0; i < nums_size; i++)
if (nums[i] <= 0 || nums[i] > nums_size)
nums[i] = 1;
for (int i = 0; i < nums_size; ++i) {
int y = abs(nums[i]);
if (nums[y - 1])
nums[y - 1] *= -1;
}
for (int i = 0; i < nums_size; ++i)
if (nums[i])
return i + 1;
return nums_size + 1;
}
int main() {
int n1[] = {1, 2, 0}, n2[] = {3, 4, -1, 1}, n3[] = {7, 8, 9, 11, 12};
printf("%d\n", firstMissingPositive(n1, 3)); // expect: 3
printf("%d\n", firstMissingPositive(n2, 4)); // expect: 2
printf("%d\n", firstMissingPositive(n3, 5)); // expect: 1
}
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