1. Two Sum

Num: 7

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

void main() {
  final s = Solution();
  // final res1 = s.twoSum([2, 7, 11, 15], 9);
  // print(res1);
  // final res2 = s.twoSum([3, 2, 4], 6);
  // print(res2);
  // final res3 = s.twoSum([3, 3], 6);
  // print(res3);
  //
  // final res21 = s.twoSum2([2, 7, 11, 15], 9);
  // print(res21);
  // final res22 = s.twoSum2([3, 2, 4], 6);
  // print(res22);
  // final res23 = s.twoSum2([3, 3], 6);
  // print(res23);

  final res31 = s.twoSum3([2, 7, 11, 15], 9);
  print(res31);
  final res32 = s.twoSum3([3, 2, 4], 6);
  print(res32);
  final res33 = s.twoSum3([3, 3], 6);
  print(res33);

}


class Solution {

  List<int> twoSum4(List<int> nums, int target) {
    final myMap = {};
    for (int i = 0; i < nums.length; i++) {
      if (myMap.containsKey(target - nums[i]) && myMap[target - nums[i]] != i) {
        return [i, myMap[target - nums[i]]];
      }
      myMap[nums[i]] = i;
    }

    return [];

  }

  List<int> twoSum3(List<int> nums, int target) {
    final myMap = {};
    for (int i = 0; i < nums.length; i++) {
      myMap[nums[i]] = i;
    }

    for (int i = 0; i < nums.length - 1; i++) {
      if (myMap.containsKey(target - nums[i]) && myMap[target - nums[i]] != i) {
        return [i, myMap[target - nums[i]]];
      }
    }

    return [];
  }

  List<int> twoSum2(List<int> nums, int target) {
    for (int i = 0; i < nums.length - 1; i++) {
      int pair = target - nums[i];
      if (nums.contains(pair)) {
        int pairIdx = nums.indexOf(pair, i + 1);
        if (pairIdx == -1) {
          continue;
        }

        if (pairIdx != i) {
          return [i, pairIdx];
        }

      }
    }
    return [];
  }

  List<int> twoSum(List<int> nums, int target) {

    for (int i = 0; i < nums.length - 1; i++) {
      for (int j = i + 1; j < nums.length; j++) {
        if (nums[i] + nums[j] == target) {
          return [i, j];
        }
      }

    }
    return [];
  }
}