[leetcode]2sum,3sum,4sum總結
阿新 • • 發佈:2018-12-10
刷了50題了,本來是想50題一起總結的,發現並沒有啥耐心。還是邊刷邊總結吧。
2sums
class Solution { public int[] twoSum(int[] nums, int target) { Map<Integer,Integer> map=new HashMap<>(); for(int i=0;i<nums.length;i++){ int remain=target-nums[i]; if(!map.containsKey(remain)){ map.put(nums[i],i); } else{ int j=map.get(remain); return new int[]{j,i}; } } return null; } }
3sums
class Solution { public List<List<Integer>> threeSum(int[] nums) { Arrays.sort(nums); List<List<Integer>> res=new ArrayList<>(); for(int i=0;i<nums.length;i++){ if(i!=0 && nums[i]==nums[i-1])continue; int p=i+1; int q=nums.length-1; while(p<nums.length&&q<nums.length&&p<q){ if(nums[p]+nums[q]<0-nums[i]){ p++; } else if(nums[p]+nums[q]>0-nums[i]){ q--; } else{ List<Integer> list=new ArrayList<>(); list.add(nums[i]); list.add(nums[p]); list.add(nums[q]); res.add(list); while(p+1<nums.length&&nums[p+1]==nums[p]){ p++; } p++; } } } return res; } }
3sums closest
class Solution { public int threeSumClosest(int[] nums, int target) { Arrays.sort(nums); int min=Integer.MAX_VALUE; int res=Integer.MAX_VALUE; for(int i=0;i<nums.length;i++){ if(i!=0 && nums[i]==nums[i-1])continue; int p=i+1; int q=nums.length-1; while(p<nums.length&&q<nums.length&&p<q){ if(nums[p]+nums[q]<target-nums[i]){ if(Math.abs(target-nums[p]-nums[q]-nums[i])<min){ min=Math.abs(target-nums[p]-nums[q]-nums[i]); res=nums[p]+nums[q]+nums[i]; } p++; } else if(nums[p]+nums[q]>target-nums[i]){ if(Math.abs(target-nums[p]-nums[q]-nums[i])<min){ min=Math.abs(target-nums[p]-nums[q]-nums[i]); res=nums[p]+nums[q]+nums[i]; } q--; } else{ return target; } } } return res; } }
4sums
class Solution {
public int threeSumClosest(int[] nums, int target) {
Arrays.sort(nums);
int min=Integer.MAX_VALUE;
int res=Integer.MAX_VALUE;
for(int i=0;i<nums.length;i++){
if(i!=0 && nums[i]==nums[i-1])continue;
int p=i+1;
int q=nums.length-1;
while(p<nums.length&&q<nums.length&&p<q){
if(nums[p]+nums[q]<target-nums[i]){
if(Math.abs(target-nums[p]-nums[q]-nums[i])<min){
min=Math.abs(target-nums[p]-nums[q]-nums[i]);
res=nums[p]+nums[q]+nums[i];
}
p++;
}
else if(nums[p]+nums[q]>target-nums[i]){
if(Math.abs(target-nums[p]-nums[q]-nums[i])<min){
min=Math.abs(target-nums[p]-nums[q]-nums[i]);
res=nums[p]+nums[q]+nums[i];
}
q--;
}
else{
return target;
}
}
}
return res;
}
}