Leetcode•Mar 19, 2026
Target Sum
Hazrat Ali
Leetcode
You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers.
- For example, if
nums = [2, 1], you can add a'+'before2and a'-'before1and concatenate them to build the expression"+2-1".
Return the number of different expressions that you can build, which evaluates to target.
Example 1:
Input: nums = [1,1,1,1,1], target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3
Example 2:
Input: nums = [1], target = 1 Output: 1
Solution
var findTargetSumWays = function(nums, target) {
let memo = new Map();
function dfs(i, sum) {
let key = i + "," + sum;
if (memo.has(key)) return memo.get(key);
if (i === nums.length) {
return sum === target ? 1 : 0;
}
let add = dfs(i + 1, sum + nums[i]);
let subtract = dfs(i + 1, sum - nums[i]);
memo.set(key, add + subtract);
return memo.get(key);
}
return dfs(0, 0);
};