feat: add question 84

Author: yinxin630

84.柱状图中最大的矩形.js

@@ -0,0 +1,30 @@
+/*
+ * @lc app=leetcode.cn id=84 lang=javascript
+ *
+ * [84] 柱状图中最大的矩形
+ */
+
+// @lc code=start
+/**
+ * @param {number[]} heights
+ * @return {number}
+ */
+var largestRectangleArea = function(heights) {
+    let result = 0;
+    const stack = [-1];
+    for (let i = 0; i < heights.length; i++) {
+        while (stack[stack.length - 1] !== -1 && heights[stack[stack.length - 1]] >= heights[i]) {
+            const j = stack.pop();
+            result = Math.max(result, heights[j] * (i - stack[stack.length - 1] - 1));
+        }
+        stack.push(i);
+    }
+
+    while (stack[stack.length - 1] !== -1) {
+        const j = stack.pop();
+        result = Math.max(result, heights[j] * (heights.length - stack[stack.length - 1] - 1));
+    }
+
+    return result;
+};
+// @lc code=end