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  • LeetCode-Two Sum III

    Design and implement a TwoSum class. It should support the following operations: add and find.

    add - Add the number to an internal data structure.
    find - Find if there exists any pair of numbers which sum is equal to the value.

    For example,

    add(1); add(3); add(5);
    find(4) -> true
    find(7) -> false
    
     
     Analysis:
    Use O(1) add and O(n) find.
     
    Solution:
    public class TwoSum {
        HashMap<Integer,Integer> numCounts = new HashMap<Integer,Integer>();
        List<Integer> nums = new ArrayList<Integer>();
    
        // Add the number to an internal data structure.
        public void add(int number) {
            if (numCounts.containsKey(number)){
                numCounts.put(number,numCounts.get(number)+1);
            } else {
                nums.add(number);
                numCounts.put(number,1);
            }
        }
    
        // Find if there exists any pair of numbers which sum is equal to the value.
        public boolean find(int value) {
            for (int num : nums){
                int otherNum = value - num;
                boolean validPair = (otherNum==num) ? (numCounts.get(num)>=2) : numCounts.containsKey(otherNum);
                if (validPair){
                    return true;
                }
            }
            return false;
        }
    }
    
    
    // Your TwoSum object will be instantiated and called as such:
    // TwoSum twoSum = new TwoSum();
    // twoSum.add(number);
    // twoSum.find(value);
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  • 原文地址:https://www.cnblogs.com/lishiblog/p/5858583.html
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