g1501_1600.s1539_kth_missing_positive_number.Solution Maven / Gradle / Ivy

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package g1501_1600.s1539_kth_missing_positive_number;

// #Easy #Array #Binary_Search #Binary_Search_I_Day_6
// #2022_04_10_Time_0_ms_(100.00%)_Space_42.1_MB_(82.14%)

/**
 * 1539 - Kth Missing Positive Number\.
 *
 * Easy
 *
 * Given an array `arr` of positive integers sorted in a **strictly increasing order** , and an integer `k`.
 *
 * _Find the_ k^th _positive integer that is missing from this array._
 *
 * **Example 1:**
 *
 * **Input:** arr = [2,3,4,7,11], k = 5
 *
 * **Output:** 9
 *
 * **Explanation:** The missing positive integers are [1,5,6,8,9,10,12,13,...]. The 5^th missing positive integer is 9.
 *
 * **Example 2:**
 *
 * **Input:** arr = [1,2,3,4], k = 2
 *
 * **Output:** 6
 *
 * **Explanation:** The missing positive integers are [5,6,7,...]. The 2^nd missing positive integer is 6.
 *
 * **Constraints:**
 *
 * *   `1 <= arr.length <= 1000`
 * *   `1 <= arr[i] <= 1000`
 * *   `1 <= k <= 1000`
 * *   `arr[i] < arr[j]` for `1 <= i < j <= arr.length`
**/
public class Solution {
    public int findKthPositive(int[] arr, int k) {
        int missed = 0;
        for (int i = 0; i < arr.length; i++) {
            if (i == 0) {
                missed += arr[0] - 1;
                if (missed >= k) {
                    return k;
                }
            } else {
                missed += arr[i] - arr[i - 1] - 1;
                if (missed >= k) {
                    missed -= arr[i] - arr[i - 1] - 1;
                    int result = arr[i - 1];
                    while (missed++ < k) {
                        result++;
                    }
                    return result;
                }
            }
        }
        int result = arr[arr.length - 1];
        while (missed++ < k) {
            result++;
        }
        return result;
    }
}