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编辑距离，，== 一边dp一边记录前驱太累，，还是dp后找路径大法好

#include<iostream>
#include<cstdio>
#include<vector>
#include<string.h>
using namespace std;
#define ll int
#define N 1010
char s[N], t[N];
int dp[N][N], n, m;
// 0为插入 1为删除 2 3为替换
struct node{
	int op;
	int pos; char c;
	node(int A=0,int E=0,char D=0):op(A),pos(E), c(D){}
	void put(){
		if(op== 2)
			printf("REPLACE %d %c\n", pos, c);
		else if(op == 0)
			printf("INSERT %d %c\n", pos +1, c);
		else if(op == 1)
			printf("DELETE %d\n", pos);
	}
}P;
void dfs(int a, int b){
	if(a == 0 && b==0)return ;
	if(s[a] == t[b] && dp[a-1][b-1] == dp[a][b])
		dfs(a-1, b-1);
	else
	{
		if(a && dp[a-1][b] +1 == dp[a][b])
		{
			P = node(1, a);
			P.put();
			dfs(a-1, b);
		}
		else if(b && dp[a][b-1] +1 == dp[a][b])
		{
			P = node(0, a, t[b]);
			P.put();
			dfs(a, b-1);
		}
		else if(a && b && dp[a-1][b-1] +1 == dp[a][b])
		{
			P = node(2, a, t[b]);
			P.put();
			dfs(a-1, b-1);
		}
	}
}
void input(){
	scanf("%s", t+1);
	n = strlen(s+1);
	m = strlen(t+1);
}
int main(){
	int i, j;
	while(~scanf("%s", s+1)){
		input();
		dp[0][0] = 0;
		for(i = 1; i <= n; i++)
			dp[i][0] = i;
		for(i = 1; i <= m; i++)
			dp[0][i] = i;
		for(i = 1; i <= n; i++)
			for(j = 1; j <= m; j++)
				dp[i][j] = min(min(dp[i-1][j], dp[i][j-1])+1, dp[i-1][j-1] + (s[i]!=t[j]));
		printf("%d\n", dp[n][m]);		
		dfs(n, m);
	}
	return 0;
}