[LeetCode 41]First Missing Positive

题目链接：first-missing-positive

/** * Given an unsorted integer array, find the first missing positive integer.For example,Given [1,2,0] return 3,and [3,4,-1,1] return 2.Your algorithm should run in O(n) time and uses constant space. * */public class FirstMissingPositive {//156 / 156 test cases passed.//Status: Accepted//Runtime: 235 ms//Submitted: 0 minutes agopublic int firstMissingPositive(int[] A) {if(A.length == 0)return 1;for (int i = 0; i < A.length; i++) {int j = A[i];while( j > 0 && j < A.length && A[j] != j) {exch(A, i, j);j = A[i];}}for(int i = 1; i < A.length; i++) {if(A[i] != i) return i;}return (A[0] == A.length) ? A.length + 1 : A.length;}public void exch(int[] A, int i, int j) {int temp = A[i];A[i] = A[j];A[j] = temp;}public static void main(String[] args) {}}

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