1. Answer map
Map each value to the first larger value after it.
const nextGreater = new Map()Typorithm · easy
Next Greater Element
next-greater-elementmonotonic-stackdecreasing-stackmapnext-greater
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Next Greater Element
Monotonic Stack
Keep a decreasing stack; each new number resolves every smaller value below it, recorded in a map for lookup.
Scan nums2 keeping a stack of values still waiting for a larger one to appear.
When a new number is bigger than the stack top, it is that value's next-greater element, so pop and record it.
Finally map each query in nums1 through the answer map, defaulting to -1.
01
Stack stays decreasing.
02
New number resolves smaller tops.
03
Map answers, default to -1.
function nextGreaterElement(nums1, nums2) {
const nextGreater = new Map();
const stack = [];
for (const num of nums2) {
while (stack.length > 0 && stack[stack.length - 1] < num) {
nextGreater.set(stack.pop(), num);
}
stack.push(num);
}
return nums1.map((num) => nextGreater.get(num) ?? -1);
}Read the implementation
Connect each part of the code to the concept before you type.
2. Resolve smaller
The current number is the next-greater for every smaller value on top.
while (stack.length > 0 && stack[stack.length - 1] < num) {3. Record answer
Pop and map each resolved value to num.
nextGreater.set(stack.pop(), num)4. Lookup with default
Values with no greater element default to -1.
nums1.map((num) => nextGreater.get(num) ?? -1)A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.