Given an unsorted integer array, find the smallest missing positive integer.
Example 1:
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Input: [1,2,0]
Output: 3
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Example 2:
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Input: [3,4,-1,1]
Output: 2
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Example 3:
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Input: [7,8,9,11,12]
Output: 1
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Note:
Your algorithm should run in O(n) time and uses constant extra space.
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class {
public int firstMissingPositive(int[] nums) {
if (nums == null || nums.length == 0) return 1;
for (int i = 0; i < nums.length;) {
int n = nums[i];
if (n > 0 && n < nums.length) {
if (nums[n - 1] != n) {
nums[i] = nums[n - 1];
nums[n - 1] = n;
i--;
}
}
i++;
}
for (int i = 0; i < nums.length; i++) {
if (nums[i] != i + 1) {
return i + 1;
}
}
return nums.length + 1;
}
}
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