给定一个整数，从整数中去掉k个数字，要求剩下的新整数尽可能小。给定的整数大小可以超过long类型的范围，所以需要用字符串来表示。

coderacademyonline · coderacademyonline · commit dd3968e69848 · 2018-11-30T11:04:46.000+08:00
diff --git a/java-leetcode/src/leetcode/str/RemoveKDigits.java b/java-leetcode/src/leetcode/str/RemoveKDigits.java
@@ -0,0 +1,132 @@
+package leetcode.str;
+
+/**
+ * <p>
+ *   给定一个整数，从整数中去掉k个数字，要求剩下的新整数尽可能小。给定的整数大小可以超过long类型的范围，所以需要用字符串来表示。
+ * </p>
+ *
+ * @author jwzhao
+ * @version 1.0
+ * @date 2018/11/29 14:35
+ */
+public class RemoveKDigits {
+
+    public static void main(String[] args) {
+        RemoveKDigits removeKDigits = new RemoveKDigits();
+        String num = "1432219";
+        int k = 3;
+        System.out.println(removeKDigits.removeKDigits(num, k));
+    }
+
+    public String removeKDigits(String num, int k) {
+        if (num == null || num.length() == 0 || num.length() == k) {
+            return "0";
+        }
+        if (k == 0) {
+            return num;
+        }
+
+        int newLength = num.length() - k;
+
+        char[] nums = num.toCharArray();
+        Stack stack = new Stack(nums.length);
+        for(int i=0;i<nums.length;i++){
+            String value = String.valueOf(nums[i]);
+            String stackPop = stack.peek();
+            while (k>0 && stackPop != null && (Integer.parseInt(value) < Integer.parseInt(stackPop))) {
+                // 栈顶弹出，入当前值
+                stack.pop();
+                stackPop = stack.peek();
+                k--;
+            }
+             stack.push(value);
+        }
+
+        StringBuffer buffer = new StringBuffer();
+        StringBuffer zero = new StringBuffer();
+        while (!stack.isEmpty()) {
+            String value = stack.pop();
+            if ("0".equals(value)){
+                zero.append(value);
+            }else{
+                if (zero.length() > 0){
+                    buffer.append(zero);
+                }
+                buffer.append(value);
+                zero = new StringBuffer();
+            }
+        }
+        if (buffer.length() == 0) {
+            return "0";
+        }
+        if (newLength > buffer.length()){
+            newLength = buffer.length();
+        }
+        return buffer.reverse().substring(0,newLength);
+    }
+
+    public class Stack {
+
+        /**
+         * 栈底层实现的数组
+         */
+        private String[] stacks;
+        /**
+         * 栈顶指针
+         */
+        private int top;
+
+        public Stack() {
+            stacks = new String[8];
+            top = -1;
+        }
+
+        public Stack(int maxSize) {
+            stacks = new String[maxSize];
+            top = -1;
+        }
+
+        /**
+         * 入栈
+         *
+         * @param val
+         */
+        public void push(String val) {
+            stacks[++top] = val;
+        }
+
+        /**
+         * 查看栈顶元素
+         *
+         * @return
+         */
+        public String peek() {
+            if (this.isEmpty()) {
+                return null;
+            }
+            return stacks[top];
+        }
+
+        /**
+         * 弹出栈顶元素
+         *
+         * @return
+         */
+        public String pop() {
+            if (this.isEmpty()) {
+                return null;
+            }
+            return stacks[top--];
+        }
+
+        /**
+         * 判断是否为空
+         *
+         * @return
+         */
+        public boolean isEmpty() {
+            return top == -1;
+        }
+
+    }
+}
