[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 ago

    public 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) {

	}

}

[LeetCode 41] First Missing Positive

原文：http://blog.csdn.net/ever223/article/details/44620307