const debug = require('debug')('twoSum');

const nums = [3, 2, 4];

const target = 6;

// solution1 -- O(n^2)

const solution1 = (ns, t) => {

for (let i = 0, iLen = ns.length; i < iLen; i += 1) {

for (let j = i + 1, jLen = ns.length; j < jLen; j += 1) {

if (ns[i] + ns[j] === t) {

return [i, j];

}

}

}

throw new Error('No tow sum solution');

};

debug('solution1:');

const result1 = solution1(nums, target);

debug(result1);

// solution2 -- O(n)

const solution2 = (ns, t) => {

for (let i = 0, iLen = ns.length; i < iLen; i += 1) {

const n = t - ns[i];

const idx = ns.indexOf(n);

if (idx !== -1 && idx !== i) { // attention

return [i, idx];

}

}

throw new Error('No tow sum solution');

};

debug('solution2:');

const result2 = solution2(nums, target);

debug(result2);

// solution3 -- O(n)

// trading space for speed

const solution3 = (ns, t) => {

const hashMap = {};

for (let i = 0, iLen = ns.length; i < iLen; i += 1) {

hashMap[`${ns[i]}`] = i;

}

for (let i = 0, iLen = ns.length; i < iLen; i += 1) {

const complement = t - ns[i];

if (hashMap[`${complement}`] !== undefined

&& hashMap[`${complement}`] !== i) {

return [i, hashMap[`${complement}`]];

}

}

throw new Error('No tow sum solution');

};

debug('solution3:');

const result3 = solution3(nums, target);

debug(result3);

// solution4 -- O(n)

const solution4 = (ns, t) => {

const hashMap = {};

for (let i = 0, iLen = ns.length; i < iLen; i += 1) {

const complement = t - ns[i];

if (hashMap[`${complement}`] !== undefined) {

return [hashMap[`${complement}`], i];

}

hashMap[`${ns[i]}`] = i;

}

throw new Error('No tow sum solution');

};

debug('solution4:');

const result4 = solution4(nums, target);

debug(result4);