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FindDuplicate287.java
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FindDuplicate287.java
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package Leetcode;
import java.util.Arrays;
public class FindDuplicate287 {
/**Method1: Binary search; Time: O(Nlog(N))); Space: O(1) **/
public int findDuplicate(int[] nums) {
int n = nums.length;
int start = 0;
int end = n-1;
int res = -1;
while(start <= end) {
int mid = start + (end - start) /2;
int cnt = 0;
for(int i = 0; i<n; i++) {
if(mid >= nums[i]) {
cnt ++;
}
}
if(cnt <= mid) {
start = mid + 1;
} else {
end = mid -1;
res = mid;
}
}
return res;
}
/**Method2: Two pointers; Time: O(N)); Space: O(1) **/
public int findDuplicate2(int[] nums) {
int slow = 0, fast= 0;
do {
slow = nums[slow];
fast = nums[nums[fast]];
} while(slow != fast);
slow = 0;
while (slow != fast) {
slow = nums[slow];
fast = nums[fast];
}
return slow;
}
}