finish "120. Triangle". Fix #120

Author: diguage

README.adoc

@@ -724,11 +724,11 @@
 |{doc_base_url}/0119-pascals-triangle-ii.adoc[Note]
 |Easy
 
-//|120
-//|{leetcode_base_url}/triangle/[Triangle]
-//|{source_base_url}/_0120_Triangle.java[Java]
-//|{doc_base_url}/0120-triangle.adoc[Note]
-//|Medium
+|120
+|{leetcode_base_url}/triangle/[Triangle]
+|{source_base_url}/_0120_Triangle.java[Java]
+|{doc_base_url}/0120-triangle.adoc[Note]
+|Medium
 
 |121
 |{leetcode_base_url}/best-time-to-buy-and-sell-stock/[Best Time to Buy and Sell Stock]

docs/0120-triangle.adoc

@@ -22,3 +22,19 @@ The minimum path sum from top to bottom is `11` (i.e., *2* + *3* + *5* + *1* = 1
 
 Bonus point if you are able to do this using only _O_(_n_) extra space, where _n_ is the total number of rows in the triangle.
 
+=== 解题分析
+
+image::images/0120-1.png[]
+
+一图胜千言！
+
+自底向上计算逐层每个元素的最小和。最后即可得出最小路径和。
+
+=== 思考题
+
+尝试一下动态规划的思路。
+
+=== 参考资料
+
+. https://leetcode-cn.com/problems/triangle/solution/120-san-jiao-xing-zui-xiao-lu-jing-he-by-alexer-66/[120. 三角形最小路径和 - 三角形最小路径和 - 力扣（LeetCode）]
+. https://leetcode-cn.com/problems/triangle/solution/di-gui-ji-yi-hua-sou-suo-zai-dao-dp-by-crsm/[【Java】递归，记忆化搜索，再到DP - 三角形最小路径和 - 力扣（LeetCode）]

docs/images/0120-1.png

@@ -0,0 +1,37 @@
+package com.diguage.algorithm.leetcode;
+
+import java.util.List;
+
+import static java.util.Arrays.asList;
+
+/**
+ * = 120. Triangle
+ *
+ * https://leetcode.com/problems/triangle/[Triangle - LeetCode]
+ *
+ * @author D瓜哥, https://www.diguage.com/
+ * @since 2020-02-07 23:14
+ */
+public class _0120_Triangle {
+    /**
+     * Runtime: 1 ms, faster than 99.42% of Java online submissions for Triangle.
+     * Memory Usage: 39.2 MB, less than 8.16% of Java online submissions for Triangle.
+     */
+    public int minimumTotal(List<List<Integer>> triangle) {
+        int[] sums = new int[triangle.size() + 1];
+        for (int i = triangle.size() - 1; i >= 0; i--) {
+            List<Integer> row = triangle.get(i);
+            for (int j = 0; j < row.size(); j++) {
+                sums[j] = Math.min(sums[j], sums[j + 1]) + row.get(j);
+            }
+        }
+        return sums[0];
+    }
+
+    public static void main(String[] args) {
+        _0120_Triangle solution = new _0120_Triangle();
+        List<List<Integer>> t1 = asList(asList(2), asList(3, 4), asList(6, 5, 7), asList(4, 1, 8, 3));
+        int r1 = solution.minimumTotal(t1);
+        System.out.println((r1 == 11) + " : " + r1);
+    }
+}