448. Find All Numbers Disappeared in an Array
题目链接:https://leetcode.com/problems...
一般这种类型的题要in place,要么给num[i]赋值成不在范围内的数,要么swap到对应位置。
public class Solution {
public List<Integer> findDisappearedNumbers(int[] nums) {
List<Integer> result = new ArrayList();
if(nums.length == 0) return result;
// sign as negative when find a number
for(int i = 0; i < nums.length; i++) {
int index = Math.abs(nums[i]) - 1;
nums[index] = -Math.abs(nums[index]);
}
// find positive number, whose index is not visited
for(int i = 0; i < nums.length; i++) {
if(nums[i] > 0) result.add(i + 1);
}
return result;
}
}
swap的方法见discussion:
https://discuss.leetcode.com/...
public class Solution {
public List<Integer> findDisappearedNumbers(int[] nums) {
List<Integer> result = new ArrayList();
if(nums.length == 0) return result;
// swap to correct position
for(int i = 0; i < nums.length; i++) {
while(nums[i] != i + 1 && nums[i] != nums[nums[i] - 1]) {
swap(nums, i, nums[i] - 1);
}
}
// find positive number, whose index is not visited
for(int i = 0; i < nums.length; i++) {
if(nums[i] != i + 1) result.add(i + 1);
}
return result;
}
private void swap(int[] nums, int i, int j) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
}
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