FirstMissingPositive.java

package com.dbc;

public class FirstMissingPositive {
    public int firstMissingPositive(int[] nums) {
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] <= 0) nums[i] = nums.length + 3;
        }
        for (int i = 0; i < nums.length; i++) {
            int num = Math.abs(nums[i]);
            if (num <= nums.length) nums[num - 1] = -Math.abs(nums[num - 1]);
        }
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] > 0) return i + 1;
        }
        return nums.length + 1;
    }
}