496. 下一个更大元素 I

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方案一: 暴力

var nextGreaterElement = function(nums1, nums2) {
    const m = nums1.length, n = nums2.length;
    const res = new Array(m).fill(0);
    for (let i = 0; i < m; ++i) {
        let j = 0;
        while (j < n && nums2[j] !== nums1[i]) {
            ++j;
        }
        let k = j + 1;
        while (k < n && nums2[k] < nums2[j]) {
            ++k;
        }
        res[i] = k < n ? nums2[k] : -1;
    }
    return res;
};

方案二: 单调栈 + 哈希表

var nextGreaterElement = function(nums1, nums2) {
    const map = new Map();
    const stack = [];
    for (let i = nums2.length - 1; i >= 0; --i) {
        const num = nums2[i];
        while (stack.length && num >= stack[stack.length - 1]) {
            stack.pop();
        }
        map.set(num, stack.length ? stack[stack.length - 1] : -1);
        stack.push(num);
    }
    const res = new Array(nums1.length).fill(0).map((_, i) => map.get(nums1[i]));
    return res;
};